Pregnancy

Hi everybody. I stopped my birth control about a month ago because I ran out and haven't had a chance to get it refilled yet.. So I had sex about 3 weeks ago, a week after stopping my birth control. Last week, I took a test and it said I was pregnant. However, on Saturday I started my period or what I assume is my period. It's a rather heavy flow, which is not like my periods, however I was assuming it was because i stopped my birth control. I took another test on Monday and it said pregnant, however I'm still bleeding very heavily. Any ideas?