There is something strange going on with my body and I need advice. I'm a 23 year old female, thin, and healthy. The past three weeks, right before my period and for two weeks after, I have been have been feeling nausea, dizziness, and been having mood swings (such as crying for no reason). My stomach feels as though it has swelled up to the size of a football, and is tight and feels as though it is full of air. Some days I get waves of anxiety. This has never happened to me before, ever, and I have been to the doctor and have taken pregnancy tests, but they say I'm not pregnant. I'm not constipated, just carrying around an uncomfortably large stomach. Please, any insight would be helpful.