What Causes Abnormal Vaginal Bleeding During Periods?

my wife is 21 year old. We had sex on 5 march 2011 and at that time she was having her periods. The bleeding went on till next 3 weeks. we meet a doctor for the abnormal bleeding for which the doctor asked to take DEX-PURE, PAUSE-MF & AZITHRAL for 3 days. But the bleeding still dint stop. so she gave Duoluton L for 21 days.now the bleeding has stopped. Was the bleeding a part of her periods or it was something else? Is my wife having any chance of getting pregnant. We had done a urine pregnancy test on 11 march 2011,which was negative