What Can Cause Delay In Period?

I had unprotected sex twice last month. After each sex, i took Postinor-2 as emergency contraceptive pills according to the instructions. I mean before 72 hours. on 28th november i had protected sex means my bf wore condoms. I had my last period on 1st November. Im expecting my periods now but its not coming. Am i pregnant ? Im very very scared. Please Please HELP