What Causes A Delayed Menstrual Period After Taking I-pill?

Hi...i had my last period on 20th july..We mated on 25th july and there were some leakage from condom so took i pill with in 2 hrd..then there was period like light discharge on 1sr august for 2 days. now its 23rd and my period has not yet come..can u please suggestc?