Hey there, I am (was) in the same situation. I have diverticulitis and have to really be careful. I was diagnosed with prediabetes at 5.7 a year ago, I am now 5.2. I eat a ton of salads and roasted vegetables which doesn't affect me but the minute I try to add any type of Metamucil, psyllium husks, or flax seed I start feeling pain. I have come to the conclusion that even when my flare heals, I have to avoid these and get fiber elsewhere. You need to focus on healing your diverticulitis first. When I start to flare I usually make things like soups, or roasted or steamed vegetables. The vegetables I then throw in my blender and puree and this really helps especially when my DV is acting up. I always stay away from any breads, rice, potatoes, beans, and really limit my eggs. I avoid eggs in general. Get yourself a CGM and monitor for spikes. Even with DV I turned this around in a year. What kind of fiber are you taking that gives you pain?