What Causes Stoppage In Menstruation?

Hi, i had unprotected with my boyfriend on my 18th day of my menstrual cycle , which my cycle is of 29 0r 30 days, 2hours after he unprotected sex i went to a doctor and he gave me the emergency pills, and now it is my 30th day of the cycle and i haven't seen my period. does this mean the pill didnt work? or the pill changed my period??