Hi. I'm 25. I Had A Medical Abortion On 5/6/16

Hi. I'm 25. I had a medical abortion on 5/6/16 when I was 6 weeks pregnant. I had my 2 weeks follow up where there was still a lot of tissue so I was scheduled for D&C a couple of days later. When I went for D&C it turned out I had passed majority of tissue and they were happy to let the rest pass naturally so I did not have to have the procedure. I was with my partner just once since the abortion. I was with him on 5/24/16 and condom broke. I did not think anything of this as I (stupidly) did not even think it was possible to get pregnant so quickly, so I did not get morning after pill.
I had a generic gyno check up on Monday with the same doc. My urine test was positive for pregnancy. He did an vaginal ultrasound and said the uterus was "empty". I did a pregnancy test myself today and the two lines are showing up very clearly.
Do you think it's possible I am carrying new pregnancy or is hCG showing from prev pregnancy? Is it possible the doc missed this on an ultrasound?? Please help!!!!