I Took Postinor 2 Tablets Few Hours After I Suspected

I took postinor 2 tablets few hours after I suspected some semen slipped through the condom he worn, I also took the 2nd tablet 12 hours later. I saw my period that month even though 2 days early (8th Jan). I am yet to see that of Feb even though it ought to have come since 4th Feb ( my period has been very regular before now, always 28 days). My husband has not been around so I have not had sex since my last period. What could be the problem?