What Causes Bleeding After A Surgical Abortion?

Hi I had a surgical abortion on 31 January and I was 7 weeks pregnant.I bled slightly for 1/2 days, again at 6/7 days and started bleeding again yesterday (16th Feb). I went to my checkup on 14th Feb and an ultrasound was done and I wast told everything was ok. I am worried about the onset of bleeding and slight cramping again, I took my Doxycycline antibiotics for 6 days as directed- should I be worried or is this normal?THANKS