What Causes Lack Of Menstruation After Taking I-pill?

i had a sex on 9feb2015 and i took ipill within 2hours than on 15feb i bled for 3 days usually my due date for menstrual cycle is 15 around of every month and till now 15march has gone mjhe abhi takk periods nhi hue mam i am so worried i have not taken pregnancy test and one more thing in january month i dont have sex still i bled 2 times in a month at a gap of 15days on 27jan also was the first day of my period than on 9feb i had a sex and after ipill i bled on 15feb and till now i have not undergone with my regular periods please suggest me mam what i should do ?