ovulation after a miscarriage

I had a D&C done on Thursday march 23, 5 days ago :/ my husband and I are ready to try again as soon as I stop bleeding (which I have only very very lightly) but my Q is ,how am I suppose to know when to start taking my opk?  And if I just started taking them , if i have any HCG left could that possibly give false positives? I'm just ready to get this baby making on the road again so any help is appreciated greatly !!