What Causes Vaginal Bleeding After Taking Unwanted 72?

hello i had a sex before 10 days after sex i felt that i should take unwanted 72 and i took within 72 hours. and the very next my blooding has started slowly some time blooding will be high but its going on since 8 days so please tell me whether is there any problem or is there any chance of pregnency........thank you 24 feb 2014