Because mine was a MMC, I suspect much of the HCG was already gone by the time I m/c. It had been a completely symptomless pregnancy, which should have been a warning sign. For me, a week after the m/c, my HCG was 12. I still managed to get a shadow of a line (looked like an evap) on a FRER almost 2 weeks after my m/c, and on my final bloodwork 3 weeks after the m/c it was 0. AF arrived just under 4 weeks after the m/c.
I really hope the symptoms disappear quickly for you. :HH: