I am 29 yrs old and a 3 + yr cervical cancer survivor. I too had a radical hysterectomy, followed by 25 treatments of external pelvic radiation and 3 internal treatments. I am also suffering from the same side affects of painful intercourse and GI problems. It seemed like all foods were giving me abdominal cramps and diarrhea. I visited a nutritionist who suggested may things such as taking lactaid pills when eating dairy or staying away from it all together, eating cooked vs raw vegies, eating fresh berries as opposed to citris fruits or grapes or dried fruits. She also suggested trying to put all food groups in each meal, that way not having too much of one irritating food. The food plan was very helpful. When I was on it, I was actually painfree!!! And I actually lost weight! But the problem is that I found it hard to stick to. Another good advice was to take vitamines as your body does not absorb as much nutrients when you have diarrhea.
As for the painful sex, my doctor recommended lubrication and a dialator. As well, his suggestion was to have intercourse or use dialator at least 3 times per week for at least 10 min each time. In my experience, the more times a week, the less pain. I also take estrogen vag, which helps with the driness and extensibility of the vag tissue.
Please remember, this has been my experience and the guidence I have received. I am by no way telling you to do this. Make sure you talk to your doctor about your specific case. Good luck. Please keep me posted on your progress.