Irregular period and spotting

Patient: Hil had a surgical abortion on the 1st of July 2014 due to that it was a twin pregnancy. however for the past two months l have been spotting. in September l had my period for two weeks then it stopped. after a week it started and lasted a week. I went to the doctor and she gave me nordette as I was on Yaz. I have been spotting since then. its either a tiny line less than a 1cm or I see a tiny little brownish clot or tissue like wen I bath. what could be wrong with me

Symptoms: At times a running tummy once or twice a week