Can Postinor 2 Disturb Periods?

i had unprotected sex with ma boyfriend ad took postinor 2 before 72 hrs ad it was on a saturday ad we stayed for one wk ad then we had again on sat ad sun ad i took postinor 2 again before the recommended hrs ad is this month now was supposed to get ma periods this months on 25 but they have failed so plz i need your help