What Causes Delay In Periods Inspite Of Having I Pill?

Hi doctor, i am tensed as i had an unprotected sex and after doing it, i took an i-pill widin an hours time den again i took after a day..my period date was 18th july n usually what hapens i get d period befr d date and today is 19th n im still waiting for my periods to come..doctor please suggest as i am bit worried and also i am feeling pukish..waiting for your answer..please reply as soon as possiblee