Fist period after miscarriage... is something wrong? (TMI)

I just got my period 4 1/2 weeks after my miscarriage. It was light and spotty for 4 days. I figured that was it because my periods usually only last 5 days. But day 5 (today) it got really heavy and there have been lots of small blood clots. My OB had me take a pregnancy test a week after the miscarriage to make sure my hcg was back to 0 and it was. And I haven't had unprotected sex since then so I know I'm not miscarrying again. I just can't figure out if this is normal or not.