I took an ec 7/13 my period was suppose to come 7/20 but it still hasn't came?

About EC pills...: Plan B or other emergency contraception pills can alter the menstrual bleeding for the cycle in which the pills were taken, and sometimes the next cycle too. One should be sure to check a home pregnancy test about 3 weeks after sex, to confirm non-pregnancy. Pregnancy is not likely, because emergency pills work most of the time.