Late ovulating on clomid?!

Kerry
I had my LMP on 10/27 with my first round of clomid. Tested positive on cycle day 35. I had my HCG levels tested on 11/30 and they were 148. Had them checked again on 12/4 and they were 747. Is it possible I'm not as far along as I thought based on my last period? I never had a positive ovulation kit, just kept trying anyway!