Miscarriage *trigger*

If I still had tissue leftover from a miscarriage, would I still be testing positive? I had an ultrasound done in February after a miscarriage in December. My doctor didn't tell me I still had things leftover. Now it is September. I made an appointment with a new doctor but I am wondering if something could still be left over after all this time. My periods have either been extremely light or really heavy with many small clots.