"my experience is different from many of the people posting here. i&#039;ve never been that good about tracking when i&#039;m fertile, but i do have very regular periods. several months ago, i had unprotected sex a few days after my period ended and took plan b within 72 hours. about a week before my expected period, i had very light spotting for maybe an hour. then it stopped. two weeks later, i still had not gotten my period, so i took a test, and it was positive. please realize that while plan b is highly effective (i&#039;d used it with success before and am wholeheartedly in favor of it being available to everyone on demand), it&#039;s not foolproof and shouldn&#039;t replace contraception."