Why Is My Period Delayed Despite Taking The Unwanted 72 Pill After Unprotected Sex?

Actually last month i.e may 4th i got my periods till now I don t getting my periods so this morning I used home pregnancy test then the result is negative and unfortunately this day me and my husband have unprotected sex and within hour i taken the unwanted 72 hour pill ..we are not planning kids at this moment so it worries us ..y my periods are delayed even though am not pregnant and now I have taken pill so..does this pill protects from pregnancy