Bleeding and heartbeat!

I've been bleeding since yesterday, started out brown and spotting and now it's red and kind of a lot. I went to the dr today because I'm worried and she said I'm 5 1/2 weeks and there was a flicker of a heartbeat so for now the baby is fine. She just doesn't know why I'm bleeding and can't tell me if I will end up miscarry ing or not. Anyone else have this happen and are still pregnant with healthy baby???