Seems like everyone I know who doesn't eat meat has lots of stomach problems - either gas or a tendency to get stomach bugs, a LOT. I don't know if it's connected, sometimes what the medical field SAYS and what you witness happening in reality are 2 different things! I'd say it's your diet. Personally I can't eat fruit because I feel awful from it. Even if I just happen to know a lot of people who fit one criteria, maybe YOU are just "allergic" to vegetables. I doubt it's the birth control.
Also, how old are you?? Sounds like wild hormones too! (if you are 16... or if you are 46... either way, wild hormones, different reasons! LOL!) - if you are like 30 or 35 or something, I'd rule out the hormones, but hey, you never know!
Duh... I guess you can't be 16 if you changed into a vegetarian 15+ years ago!