I, too, had very bad gas pains in the first few days after my reversal. The first night in the hospital wasn't too bad, because I was so drugged up. But the second night in the hospital, I spent the entire night walking the wards trying to alleviate the pain. Even after my bowels opened up that next morning, the gas didn't really subside, despite the fact that I must have had something around 15 bowel movements. When I got home (four days after the surgery), I still had pretty bad gas pains, similar to what you're describing, for about a month afterwards. All I can say is that I got back into pretty good shape, even without getting back to the gym, because I walked three times a day for an hour a day, just to get the gas away. It is uncomfortable as all heck, but it does, eventually, go away. I had my ileostomy for about 10 weeks only, and my surgeon told me that the gas pains are just the bowels trying to get back to normal after having (as she put it) "been on vacation" for that time.
Good luck and good recovery!