"me and my boyfriend had unprotected sex on the last day of my period. i knew the chances of getting pregnant on the last day of your period are slim but i didn&#039;t want to take any chances. therefore 30 minutes after i went ahead and bought plan b. the only side affect i experienced at first was a slim headache and it only lasted the first day. the pill also messed with my hormones and i had a huge break out on my face. the closer i got to my period i stated stressing more and the pill delayed my period by 6 days. so if you already took the pill and you&#039;re late don&#039;t worry it&#039;s the pill doing its job."