What Causes Delayed Periods After Taking Unwanted-72 Followed By Unprotected Sex?

Hi, i had sex with my husand. I took u-72 within 2 days. Again after 2 days i took the same pill due to unprotected sex. I got very light periods at regular mc date. After 15 days i had sex but not sure about discharge. It has been 28 days i have not got periods. Normally i get periods within 24-25 days. Pls sugest.