bleeding from vagina but not periods

hi, i am 23 year old girl and usually have irregular periods, I had my periods on 30th april 2013 and lasted 4 days,then i had first time protected sex on 15th may ,but for precaution in took ipill with in 7 hours. On 20th i got my periods and they lasted 4 days . I had no pain or cramps and they were very dark and dirty periods . Now from 31st may night i am bleeding with very less mucus and more blood , and blood flow is heavy like periods and for few days i am feeling very tired. Can u pls tell me the reason behind such odd happenings and wot i shud do