Took postinor 2 a day before ovulation after unprotected sex. period is 18 days late and negative urine test on the 10th day after missed expected day?

Pregnancy unlikely: Plan B, Postinor 2, and other brands of emergency contraceptive pills can alter the menstrual cycle for the cycle in which Plan B or Postinor 2 was taken, and sometimes the next month's cycle too. One should be sure to check a home pregnancy test about 3 weeks after sex, because emergency contraceptive pills work most of the time, but not all the time.