I took Postinor on the 17/02/13 abt 35hours after intercourse. I felt very tired but i did not get any withdrawal bleeding. Abt 2 weeks later 4/03/13( a few days earlier than my normal period starting date) i started bleeding and i experienced great pain at my lower back,neck and waist...the pain eventually stopped.However 2 days later the bleeding was very very little which is unusual and i did not experience any menses cramps.This is worrying...am i pregnant?!