Could I be pregnant or just having a fat belly or check another pregnancy test? Many times sex in 1 month, negative pregnancy test, I am skinny, never had a belly, I am in my 20s and suddenly I have a belly, I threw up one day. I have never had a fat belly in my life!?

Except for the "fat belly" and the throwing up one time, what are you other symptoms?

Have you had unprotected sex? When did you have your last period? Are you on birth control? Some oral contraceptives can make you gain weight. What are your eating habits like? You could just be bloated, depending on your diet and exercise, or lack thereof. Hard to know with so little details provided.