What Causes Delay In Periods With Negative Pregnancy Result?

Hi ,I got married 2 months ago.Before 3 days of wedding I took a medicine to delay my period The first month after marriage was normal , i had period on time In second month I got a little bleeding before 9 days of my period And after that I didnt get my period on time It is now 9 days late and I didnt have it I did pregnancy test but it was negative What should I do?