I think the Doctors estimated me farther along than I really am! Anyone else have a similar story?

Hello ladies! So my doctor is going off of my last period, which was 6dec. However, I didn't BD until the 14th, when my fiancé was in town, so there's NO WAY I can be the 5wk2day they keep putting me at.

TMI TIME!!:

I visited the ER on 1/7 for bright red bleeding and mild cramps on my right side. My HcG levels were 80, cervix closed. They had me come in Monday to redraw blood and do a trans vag US, since I had a M/C a few years before. My levels on 1/12 were over 800, but the U/S results were 'inconclusive'.

All panic aside, I did the math last night and realized that I am, at the most 29 days past when I COULD have made baby, not this 37 days they're estimating me at. (Which would explain the lousy U/S results, but leaves me rather high in the week 4 hgh levels chart).

TL;DR,

I think my doctor thinks I'm more pregnant than I am, anyone else have this happen to them?