What Causes Positive Pregnancy Test After Abortion?

I reaaly need some help figuring this out. I haven't had unprotected sex but I have a pregnancy test that came up positive, I also have 5 others that are negative (digital) . I had an abortion in may and the past few weeks were the first since the procedure that I didnt feel pregnant. My period is due next week but I'm really scared and I need some support.