I have had UC for 30 years and diagnosed with PSC 10 years ago. I take Culturelle daily I've tried quite a few probiotics and that has been one of the best for me. From time to time I will also drink a Kombucha, this is a tea with live probiotic cultures. GT's Synergy line seems to be the most consistent, but not for the faint of heart, think tea with some sour fruit juice mixed in, it is an acquired taste.
As for Celiac disease, for years I have known that pizza and pasta bother me after I eat them. I think now that it may be the gluten and not the tomato sauce I had always blamed it on. A few years ago when I heard a neighbor talking about their son's "wheat allergy" I started looking up some information about celiac, and started to move to a more gluten free diet.
I only have personal anecdotal evidence; however avoiding gluten makes me feel better. I told my primary that I felt this way, he tested me for celiac disease and it was negative. He told me "If you feel better when you avoid wheat products, then avoid them, there isn't a reason for me to tell to eat wheat.".
I would recommend at least trying a diet low in gluten. It's not that difficult, it may seem daunting at first but there's not gluten in meats, fruits and vegetables. Eggs for breakfast, salad for lunch, and a piece of meat and vegetables for supper is gluten (and lactose) free. Some of the snacks I've come to enjoy are Kind and Larabars, along with dates, raisins, and nuts. Just avoid fried foods, bread, oatmeal, wheat cereals, pasta, and pastries almost all candy.
The most difficult thing has been eating gluten free and feeling great for months then to have PSC symptoms it was really depressing. I had to remember I was not curing PSC, I still have it. If I'm reducing my symptoms and frequency of problems it is still worth it.