What Leads To Positive UPT Inspite Of Having An Abortion?

I had an abortion on Feb 7. I went to get on the birth control shot 3 weeks later. Still showed I was pregnant. I had PROTECTED sex twice. They took my blood and it came back showing I was 6 weeks pregnant. When I had the abortion I was 7 weeks 1 day. I went back to the abortion clinic and they gave me an ultra sound. It showed a blood clot and she said it kinda looked like an early pregnancy but the tissue didn t look to appear as if I were pregnant. She confused me really bad. Anyway, so she gave me pills again. I barely bleed the second time. Today will be exactly 6 weeks since I had the first abortion. I got a pregnancy test about an hour ago and it s still showing a faint line. I have not had any sex at all since before the second set of pills I took. I m really confused?