What Causes Bleeding With A Positive Pregnancy Test?

hi doctor i m 18 plus. i was pregnant in november 2011 and at that time i have taken unwanted 72. later on in this january 2012 i become pregnant again and at that i also take with unwanted 72. from last month again i m pregnant and last mc date was 26-29. the day i was checked with pregnancy tube,its showed me positive again i went to hospital for a checkup.the result was also positive .but at the same day i had bleeding which was more at the same day and after next day bleeding was very less. now i m confused that what is going on inside.