Positive Pregnancy test!!

I found out I was pregnant in June... July 22nd I found out that I was miscarrying and it was a blighted ovum ( meaning everything was developing but the baby) I had to have a D&C on July 29th. Yesterday was my follow up appointment and they took a pregnancy test and my Doctor said it was a strong positive. Me and my husband have had sex but we used condoms. Is it normal to still get a postlitive test 3 weeks after? We did start w/o a condom once but we eventually put on a condom. Should I b worried something else is wrong?? Because I seriously do not thing Im pregnant!!