"me and my boyfriend had unprotected sex the second day of my period. 20 to 24 hours later i took plan b. i had nausea select days over a week or two then everything seemed back to normal. two days after i had unprotected sex my period stopped. plan b works three different ways one of them being telling your body not to ovulate. well 11 days after my period stopped i was due to ovulate. plan b more than likely told my body not to ovulate at that time because my period was 9 days late. i&#039;m also overweight by a couple pounds to where plan b effectiveness starts to fade. i think because i was ovulating close to when i took plan b it told my body to wait to ovulate. today i got my period. thank goodness!!"