I have had my period twice this month, the last time i had sex was valentines day but 15 minutes after having sex i took the emergency pill?

It happens...: Emergency contraception pills (such as Plan B and other brands) can alter the menstrual for the cycle in which Plan B was taken, and sometimes the next cycle too. One should be sure to check a home pregnancy test about 3 weeks after sex, because Plan B works most of the time, but not all the time. Also, be sure to start using a reliable form of birth control, so that one will not need Plan B.