15 days been periods? 4 AF's in 2 mths.

Is this normal or healthy? It's been going like this more or less for 2 months like clock work. 4 periods in two months. I was suspicious of pregnancy, so I took a pregnancy test about 3 weeks ago. It came out positive, but then I took 2 tests the other day and it came out negative. I'm bleeding more than normal. I gained six pounds recently and (tmi) but, two months ago my boobs became veiny, full and sensitive and they have been this way regardless of whether I'm bleeding or not . I get headaches a lot and feel like I'm going to faint after I eat. I'm making a doctor's appointment tomorrow, but in the mean time what do you think is going on?