What Are the First Signs of a Diverticulitis Flare And What Should You Do?

This article does not constitute medical advice. Medical advice should always be sought from a qualified medical practitioner. This article is based on anonymised discussions from our community group on Facebook.

For most people, the first sign of a diverticulitis flare is pain in the lower abdomen, most commonly on the left side. However, our community discussions show that symptoms can vary widely. Some people experience right-sided pain, back pain, bloating, constipation, diarrhoea, nausea, urinary symptoms or even headache before the abdominal pain becomes obvious.

Just as importantly, there is real confusion about what to do when these symptoms begin. That confusion matters, because acting at the right moment can be the difference between managing a flare at home and ending up in hospital.

Below, we bring together the experiences shared in our community alongside current clinical understanding of diverticular disease, including practical insights our members have found genuinely useful but rarely been told by their doctors.

Is Left-Sided Pain Always The First Sign?

Often, but not always.

Many members described a familiar pattern: a dull ache in the lower left abdomen, increasing tenderness, bloating and wind, and a change in bowel habits. This aligns with medical understanding. In the UK, diverticulitis most commonly affects the sigmoid colon, which sits on the lower left side.

However, several members reported right-sided pain.

“Margaret from Lancashire” described it simply as pain in the left side. “June from Kent” said the same. “Andrew from Devon” said his flares begin with right-sided pain and bloating. “Madeline from Birmingham” added: Everyone gets left side pain, but I always get the right side.

“Extreme cramping, bloating, explosive bowel movements, and then the fever. When the fever comes, I know it is an infection. That is when I need antibiotics. — Sandra, New South Wales”

Right-sided diverticulitis is less common in Western populations but does occur. Pain patterns can also reflect referred pain or individual anatomy.

Can Back Pain Be An Early Warning Sign?

Yes.

A number of members reported back pain before abdominal pain. “Roxanne from Cardiff” described severe right lower back pain that later moved to the front. “Dennis from Essex” said the pain starts in his back and travels around to the left side. “Brenda from York” mentioned hip pain when her flare becomes severe.

This can be confusing, particularly for those who initially suspect kidney issues or musculoskeletal problems. Lower back discomfort alongside abdominal symptoms should not be ignored, especially if you have a history of diverticulitis.

What About Bloating, Gas And Bowel Changes?

For many, the first sign is not pain but pressure.

Members described: a sensation of a balloon inflating in the lower abdomen, excessive wind, constipation, diarrhoea, and alternating constipation and diarrhoea. “Bev from Nottingham” described the feeling as “someone inflating a balloon inside me until it feels like it will explode.” She admitted she feared cancer before receiving a diagnosis.

Several members mentioned constipation first, followed by cramps. Others experienced diarrhoea early on. This overlap with irritable bowel syndrome causes genuine confusion. “Nancy from Surrey,” who also has IBS, found the symptoms almost identical. Her flare was only identified through a CT scan performed for another reason.

“My warning signs are firstly bloating like I am pregnant, then my bowel becomes agitated and very angry. When the fever arrives on top of that, I know it is time. But often I can manage it for a day or two on just water and lemonade. Stress is always a factor for me. — Sandra, New South Wales”

Are There Less Obvious Early Symptoms?

Yes, and these can catch people off guard.

Some members reported: headache before abdominal pain, feeling feverish, nausea, loss of appetite, dry mouth, increased urinary urgency, and a pounding or racing heart. “Jean from Oxford” said a dull headache is her first clue. “John from Norfolk” mentioned urinary urgency with lower abdominal discomfort. “Mary from Bristol” described her heart pounding, which she found frightening.

One member described the early signs as: a high temperature, exhaustion, abdominal pain to the point of being unable to stand upright, mucus stools, and a very noisy gut with lots of gurgling. Another simply said she shivers, even in hot weather, as her early signal.

Inflammation in the pelvis can irritate the bladder, explaining urinary symptoms. Systemic inflammation can cause general unwellness, fatigue and feverish feelings.

Why Does Each Flare Feel Different From The Last?

This is one of the most common and least discussed aspects of living with diverticulitis, and it comes up repeatedly in our group.

“The doctor who treated me said that it varies with each flare-up. So what I can expect is different pain each time. I just did not know how to judge whether I needed antibiotics, a GP visit, or hospital. — Rachel, Minnesota”

The clinical picture behind this is well established. A 2023 review in the journal Cureus, “Tips for the Medical Management of Diverticulitis” (Yoo et al., PMC10065882), confirms that diverticulitis exists on a spectrum from mild uncomplicated inflammation to complicated disease involving abscess, perforation or sepsis. Individual episodes can sit anywhere on that spectrum, which is why a flare that felt manageable at home last year might need hospital treatment this time.

Several members found this deeply unsettling. Not knowing what to expect made it harder to trust their own judgement. Understanding that the severity genuinely varies each time is not a failure to pay attention. It is the nature of the condition.

How Quickly Can A Flare Become Serious?

This is where community experience becomes especially important.

One member described mild side pain and unusual shooting pains which she initially attributed to menopause. She continued working, hosted a party and felt embarrassed about seeking help. Within days, she was admitted to hospital with a sealed perforation and sepsis from burst abscesses. She described feeling traumatised afterwards and now seeks help much earlier.

“I waited and my bowel ruptured. Do not live with regrets. — Pauline”

“I tried to wait it out and then suddenly my bowel perforated. Do not delay in getting medical help. — Anonymous Member, Diverticulitis Club”

These accounts are not shared to frighten anyone. They are shared because several members said they wished someone had told them earlier that diverticulitis can escalate without warning.

According to the NHS, you should seek urgent medical attention if you experience: severe or worsening abdominal pain, high temperature, persistent vomiting, blood in stools, or signs of sepsis such as confusion or extreme weakness. You can read more about complications on the NHS diverticular disease page.

Should I Worry If I Don’t Have A Fever?

One of the most repeated questions in our group is whether a fever confirms a serious infection. The short answer is: fever strongly suggests infection, but its absence does not rule out a serious problem.

“The best way to know if you need antibiotics is if you have a fever alongside your pain. My doctor told me that a high temperature is a sign of infection, which needs to be treated with antibiotics to stop it progressing. — Kelly”

Multiple members confirm this. Fever plus severe pain is a strong signal to seek medical assessment without delay. But several members reported going to hospital without a fever and finding they needed emergency surgery or had perforated bowel.

“I did not have a fever and no blood in my stools. I went to the emergency room. They took me straight to emergency surgery. — Diane, Florida”

“I didn’t have a fever but ended up having emergency surgery and spent 16 days in hospital due to sepsis. Please go. — Barbara, Texas”

The clinical evidence supports this. According to the Yoo et al. review referenced above, a raised C-reactive protein (CRP) level is a key inflammatory marker used alongside white blood cell count to help diagnose diverticulitis and its complications. The presence of a fever is helpful, but clinicians rely on multiple factors, not fever alone.

“I never get a fever when I have an attack. It is the pain that tells me when I need medical help. — Elaine, Scotland”

If your pain is severe, escalating, or unlike anything you have experienced before, seek medical advice even without a fever.

What Is A CRP Blood Test And Can I Ask For One?

This is a practical tip that came up strongly in our community and that many members said they had never been told about.

CRP stands for C-reactive protein. It is a substance produced by the liver in response to inflammation. During a diverticulitis flare, CRP levels typically rise significantly. Clinicians use this alongside symptoms to help assess how serious a flare is and whether antibiotics or hospital admission are needed.

“Ask your doctor about the CRP blood test. It rises with inflammation. After my massive attack, they gave me a blood test form so I could go and have a test whenever I suspected a bad flare-up. You really do not want to be taking antibiotics without knowing whether you have an infection. — Patricia, County Cork”

“My CRP was 172 when I went in with sepsis. Ten weeks after surgery it was 1.5, back in the normal range. — Dave, UK”

If you have had a confirmed diagnosis of diverticulitis and you are having recurrent flares, it is worth asking your GP whether a standing blood test request could be arranged so you can get a CRP tested quickly when you suspect a flare. Not every GP surgery will offer this, but it is a reasonable question to ask, and it can help avoid unnecessary antibiotic use as well as dangerous delays.

What Do People Do At The First Sign Of A Flare?

This was the second half of the original question, and many members felt it was overlooked when they were first diagnosed.

1. Switching To Clear Liquids

Several members move to clear liquids for two to three days at the first sign of pain. Broths, water and weak tea were commonly mentioned.

“At the first sign of pain I stop eating entirely for a day and drink plenty of water. Then I introduce bone broth, clear apple juice, black tea. After three days of that, I start soft foods: mash, well-cooked carrots, white pasta, plain chicken, soups. I add one new food at a time and keep a food diary to track what triggers things. — Helen, Texas”

This approach mirrors clinical guidance. The Yoo et al. review notes that a clear liquid diet is recommended during the acute phase to rest the bowel, with diet advancing as symptoms improve.

2. Moving To Soft Or Low Residue Foods

After initial bowel rest, members reported introducing: scrambled eggs, cottage cheese, tinned fruit, light soups, white rice and mashed potato. “Monica from Leeds” follows a low residue diet and takes antibiotics when prescribed.

3. Gentle Movement

A few members mentioned gentle walking to relieve gas and reduce bloating. Several said that slow movement around the house helped more than lying still all day.

4. Warmth

Heat pads were frequently mentioned to ease cramps. Warm baths were also suggested.

5. Pain Relief – And What Not To Take

Paracetamol was consistently recommended within safe dosing limits. Some mentioned co-codamol but were mindful of its constipating effect.

Important: Non-steroidal anti-inflammatory drugs such as ibuprofen and aspirin are strongly discouraged in diverticular disease. Several members reported being told to take ibuprofen by a GP or out-of-hours service and found it made their symptoms significantly worse. Research supports this concern: NSAIDs may increase the risk of complications including bleeding and perforation. Always check with a healthcare professional before taking any pain relief during a flare.

“Ibuprofen is a definite no with diverticular disease. It can cause bleeding, an abscess or a flare. My doctor told me to take it. He was negligent. Never again. — Suzanne, Cork”

6. Seeking Medical Review

Those who had experienced severe complications stressed the importance of early medical review rather than waiting it out. Several said they now go sooner than they used to.

7. Asking About A Rescue Pack

A smaller number of UK members mentioned a pre-arranged “rescue pack” of antibiotics that can be collected and taken at the first sign of a confirmed flare, without needing to wait for a GP appointment.

“A 111 duty doctor told me about something called a rescue pack. I tried to get one from my GP but was told my gastroenterologist needed to recommend it first. It is worth asking the team who manages you in hospital, as it can save you sitting in A&E for hours when you know what is happening. — Fiona, Yorkshire”

This is not available to everyone and is not a substitute for medical assessment. But it is worth asking about if you have a confirmed diagnosis and a pattern of recurrent flares.

When Should You Not Try To Manage It Yourself?

You should seek medical advice urgently if:

• Pain is severe or escalating, or is the worst you have experienced
• You develop a fever, even a low-grade one
• You feel faint, confused or extremely weak
• You have persistent vomiting
• You notice significant or persistent bleeding
• Symptoms are different from your usual pattern
• You are not improving after 48 to 72 hours of bowel rest

One member wrote: “I always end up in hospital with it.” For some people, early intervention prevents escalation. Another said: “I measure the pain level from one to ten. Anything over a six and I go to the emergency department.” While there is no universal rule, having a personal threshold agreed with your GP can help.

“I suffered for three weeks and kept being fobbed off with possible UTI and constipation. Ten days after my first appointment I finally got a scan to discover I had a perforation and was in hospital for nine days on IV antibiotics. I probably would not have realised it had got that bad. Please keep pressing. — Nicky, New York”

Why Does It Feel So Unpredictable?

Because it is.

Symptoms vary in: location, intensity, speed of onset, and associated features. Some flares remain mild and settle within days. Others progress rapidly. The same person can experience very different episodes.

For people over 50, this unpredictability can be deeply unsettling. You may already be managing other health conditions. You may be caring for grandchildren or ageing parents. The idea of sudden hospital admission is frightening.

Understanding your own early warning signs, and having a plan agreed with your GP, can restore a sense of control. A food and symptoms diary is one of the most practical tools for building that picture over time.

Frequently Asked Questions

Is Left-Sided Pain Always Diverticulitis?

No. Other conditions can cause similar pain, including ovarian cysts, kidney problems and IBS. Always seek medical assessment if symptoms are new, severe or unusual.

Can IBS Mimic Diverticulitis?

Yes. The symptoms overlap significantly, which adds to the confusion many members describe. Imaging such as CT scanning is often used to confirm diverticulitis. One of our members had both conditions and could not tell them apart without a scan.

Does A Fever Mean I Definitely Need Antibiotics?

A fever alongside abdominal pain is a strong indicator of infection and you should seek medical assessment. However, current guidance suggests that in mild, uncomplicated diverticulitis in otherwise healthy adults, antibiotics may not always be needed. This is something to discuss with your doctor based on your specific circumstances.

What If I Don’t Have A Fever But I’m In Severe Pain?

Do not wait. Several members in our group have had serious complications including perforations and sepsis without a fever. Severe or escalating pain on its own is a reason to seek medical help urgently.

Should I Stop Eating Immediately?

Many clinicians advise bowel rest during acute flares. A clear liquid diet for the first two to three days, followed by a gradual return to soft foods, is a common approach. However, advice varies and should always be personalised by your own healthcare professional.

Can Back Pain Alone Be A Flare?

It can be an early sign for some people, especially if it is consistent with previous episodes and is accompanied by other symptoms. Lower back or hip pain alongside any abdominal discomfort should not be dismissed if you have a history of diverticulitis.

What Is The Difference Between Diverticulosis And Diverticulitis?

Diverticulosis is the presence of small pouches (diverticula) in the colon wall. Many people have these without any symptoms. Diverticulitis is what happens when one or more of those pouches becomes inflamed or infected, causing the symptoms described in this article.

Key Takeaways

• Lower left abdominal pain is the most common first sign, but right-sided and back pain are also reported by members.
• Bloating, constipation, diarrhoea, nausea and fatigue frequently precede or accompany pain.
• Each flare can feel different from the last, including in severity. This is normal but can be disorienting.
• A fever alongside pain strongly suggests infection, but serious complications can occur without a fever.
• CRP blood testing is a useful tool for assessing inflammation. Ask your GP whether a standing test form can be arranged.
• Ibuprofen and other NSAIDs should be avoided. Paracetamol is the recommended over-the-counter option during a flare.
• Clear liquids and bowel rest are the most commonly used first-line self-management strategies, consistent with clinical guidance.
• If you are in severe or escalating pain, have a fever, are vomiting, or have any bleeding, seek medical attention without delay.
• Understanding your own early warning signs and having a plan with your GP can make a significant difference to how quickly you respond.

If you are learning your own early warning signs, you are not alone. Thousands of members are navigating exactly these questions in our community every day.

You can join the discussion in our Living With Diverticulitis forum, or start tracking your symptoms and food with our food and symptoms diary to build your own picture over time.

Clinical reference: Yoo J, Gupta A, Bhatt N. Tips for the Medical Management of Diverticulitis. Cureus. 2023. PMC10065882. Read the paper

This article does not constitute medical advice. Medical advice should always be sought from a qualified medical practitioner.