My friend had a period up until she was four months along. Although, very uncommon, it does happen. When I started to miscarry with my last period i was bleeding like a period and my doctor said i could still have a normal pregnancy because my hCG was rising.. unfortunately it dropped later and i completed a miscarriage. but like my doc told me, you can bleed while pregnant if you're unsure.. take a test. But you could just be coming down with something.