How Does ECP Work?

How do you know the morning after pill has worked? Last feb 14 (monday), i had an unproteted sex, took map the next day.. 6 days after (sunday) i started bleeding for 6 days (until saturday).. was it already my period? or do i need to wait for the next one? btw, i used to have my period on 25 or 26th day of the month.. thanks..