Question

I had a miscarriage in November but had my next period on time which was December 15th. I found out I was pregnant a few days before my expected period which was January 10th. Anyways I went to get blood work done last Thursday and I thought I was about 4 weeks 5 day pregnant but my doctor told me based on my HCG level I'm actually around 6 weeks pregnant. I'm very confused because I would've been pregnant during my period in December. I don't think it was implantation bleeding because it was heavy with blood clots. Does anyone have any ideas? Do you add two weeks based off of the blood work? Or could the blood work not be accurate?