Period?

So, my fiance and I have been trying to get pregnant for a while now, and about a week ago I took a pregnancy test the day before my "period" and it was negative. And my period was like a week and a half early.. Then I bleed for like 5 days, but every morning for about 2 1/2 weeks I've been nauseous and I feel weak and headaches and mood swings and all that, I havent taken a test again since I figured I had my period. Is it common to have a "period" and still test positive? I'm just a little confused at this point.