Fiber feeds the good bacteria in your gut and it's the best way to boost your colonic friends.
I also take Intestinew from Renew Life (has L-Glutamine in it also, I've taken L-Glutamine for ten years without issue), Aloe Vera Gel Caps from NOW brand, and Slippery Elm. That generally fixes 90% of my GI complaints.
It sounds like you have Diverticulitis. Do you get a small fever after you eat by any chance? I also have a problem with my Sigmoid Colon and I get fevers and flu like symptoms after every meal. I had to cut out all animal products (they're constipating for me) and just eat loads of plants. It didn't cure it but has made me a lot more comfortable and given me a little more energy. I have a growth in my abdomen or hernia though and it's impacting the Sigmoid and my bladder and it is crazy uncomfortable. I can't diet or supplement my way out of that though, I have to go see the doc and probably get surgery (UGH!!!).
I always ate kinda carefully but then would have a Haagan Daz relapse or a Friday Night Pizza episode. This has actually made me start eating a lot better.