Oh, I am sorry to hear this. I have an aunt with Crohn's Disease. I also have stomach problems and have almost had some embarrassing times.
Are you sure it is related to the radiation? I found that cutting out Splenda helped me a LOT. I like the taste of it, so I was sorry to do that, but after I stopped using it, I noticed a huge improvement. Also, certain foods seem to trigger it for me- onion soup mix, for whatever reason does NOT agree with me. Try keeping a food journal and see if you can see a pattern.