Hi solomani!
I don't have ulcerative colitis or any of the other awful digestive stuff, but I might have an avenue you could go down. My daughter had low-grade diarrhea for years, awful gas, bloating. We tested and tested (Cleveland Clinic) but couldn't come up with a diagnosis, so I just did what I thought was useful, and that turned out to be the Specific Carbohydrate Diet (or "SCD" for short - both terms are google-able).
It aligns very closely with the Primal, but has a few quirks that make a difference for the daughter. After one year on the strict protocol - diarrhea, gas, bloating, all gone. Nice regular, formed, poops that don't gas-bomb the entire house. There is also another diet that bases itself on the SCD, but adds a probiotic protocol, and it is called GAPS (Gut and Psychology Syndrome). I haven't followed the GAPS with the daughter because I am adjusting the fatty acids per Primal before I dive into researching GAPS. One thing at a time, you know...
Daughter cannot have potato peels, whole seeds, stuff like that because it runs right through her. If we grind the seeds into stuff like seed/nut butters and peel the potatoes, she is fine. Hope this helps - it did the trick with us.
SCD website:
Breaking the Vicious Cycle - The Specific Carbohydrate Diet
Book is: "Breaking the Vicious Cycle" by Elaine Gottschall