Miscarriage and HCG

Hi everyone. I had my second miscarriage 18 days ago (D&C) I should have been a little over 9 weeks but baby only measured 7w3d (I hear the heart beat when it measured 7w2d)

My husband and I are eager to Start TTC asap. My Dr told me at my two week follow up we can start trying again. I bought ovulation tests today along with some more pregnancy tests. I took the ovulation test and it showed I was at my peak - I then took a first response pregnancy test and it is still showing as pregnant...is this normal after 18 days?? If HCG is still showing in my system will that prevent me from ovulating and getting pregnant if we start trying again now? Thanks!!!