L-Glutamine Powder from NOW is what I use, and it's great!
I use the suggested dosage with breakfast, lunch, 1/2 dosage at dinner, and then full dosage before bed. Within 3-5 days of inflammation/colon pain I am better.
Like you said, it's about figuring out what irritates / causes the problem in your diet and eliminating that. For me, I think it was peanut butter and I was eating a LOT of that to keep weight up.
Now I just have to get rid of the nasty bacteria!
Best of luck.
My best advice is to take steps that are measurable, don't do more than 1 thing/change per-time and track it.