Hi Sir. I Din Get My Periods I Was Due

Hi sir. I din get my periods I was due on 20 th April 2016 but its 1 st may I still din get my periods . I had sex with my partner n took I pill aftr a day I.e. after 24 hours. I m doubting that I pill has not working and because of which I have not got perids and I don want to be pregnant so soon . pls helpe