I wouldnt think you would ovulate with HCG still in your system but I'm no expert. What did you find out at your u/s? Sorry if you already posted and I missed it. I'd probably wait a little longer just to be safe- but thats just me.
from what i have read, its unlikely to o with hcg in your system. I think it depends on the individual as to how long before you get a neg on pg test, some ladies i read said it was about 2-3 weeks but i think this can vary.