There are lots and lots of different pills and different BC methods. If you've had a negative side affect from one pill, try another. I take Depo Provera injections which keeps me from ovulating and having a period all together, so I don't seem to go through the hormonal fluctuations that most of the others here do, and so my gut problems seem to stay pretty consistent (which is good because I was never regular before, so I could be enjoying surprise periods and surprise gut problems both). I have never had any side affects from it, be they sexual or weight-related. But some people do experience weight gain with Depo (but that can happen with any BC). And there is some evidence that long-term usage of it may result in bone density loss, but no one knows how long "long-term" is or if every woman is even affected. It's not been out long enough to know anything for certain. Me, I'm all but doomed to osteoporisis anyways because of genetics, but I am a bit on the heavy side and I like to walk and weight-bearing exercise is supposed to be better than calcium supplements for your bones, so I'm either in the clear or doomed anyways and don't look for the medicine to affect me one way or the other. My quality of life, right now, is better served by not having the unpredictable periods and changes in my bowel function.
NuvaRing NuvaRing NuvaRing!
Sorry, I just love this relatively new method of birth control. I've been using it for about two years after several years on the pill. It's a once-monthly vaginal ring that you insert, leave in for 3 weeks, and take out for one week before putting a new one in. Lose dose of hormones and I've never had any side effects whatsoever from it. They have a website, nuvaring.com, where you can learn more about it.
A lot of women do experience more gut problems with ovulation. I've never really been constipated so I can't give you much advice there but maybe start increasing your fluid and fiber intake around the days you ovulate; might get things moving faster.
NuvaRing NuvaRing NuvaRing!
Sorry, I just love this relatively new method of birth control.