What Causes A Delayed Menstrual Period?

I have a question. The last time i got my period was on the end of july and the biggining of august. then i had sex 4 days after my period and me and my partner used a condom. We thought it broke so the next day after sex i went to go get the after pill. Then a week later i started getting a brown goy thing with a little bit of blood. Since then i havent gotten my period. Can you help me out please.