What Causes Early Pregnancy Symptoms?

Hi, i'm twenty. I went on depro provera and I'm due for my next shot in a week. The first two months I bleed constantly. it has stopped entirely. I was on antibiotic before the bleeding stopped. I'm now getting pms?possible early pregnancy symptoms? I took a pregnancy test last week and it came back negative, but my husband and I have sex almost everyday, sometimes multiple times unprotected, and I was wondering if I could be pregnant