Answers to your plan b questions: ( sorry it is long)
You can get pregnant at any time during your monthly cycle—from the start of one period to the beginning of the next. Although people talk about a “safe time of the month,” it’s hard to tell when this is, for many reasons.
Your most fertile time of the month is when you’re ovulating (producing an egg), but most women aren’t aware when this is happening. Also, it takes several days for an egg to make its way from the ovary down the Fallopian tube, and an egg can be fertilized at any point during this journey. Sperm can survive in a woman’s body for up to seven days, so even if you hadn’t ovulated when you had sex, the sperm could still fertilize the egg sometime afterwards.
Many women don’t have regular periods. The time between your periods can vary, depending on what’s happening in your life, whether you’re stressed, and whether or not you’re eating properly. This makes it even more difficult to calculate your “safe” time.
When accidents happen, such as a condom breaking, and you don’t want to get pregnant, emergency contraception is there as a backup. It’s not something you should use regularly, and you should never think of it as an alternative to a long-term method of birth control.
The sooner you take plan B®, the more effective it is. It can prevent pregnancy if taken within 72 hours and preferably within 12 hours of unprotected sex. If you take it within 24 hours of unprotected sex, it is 95% effective. If you take it between 48 and 72 hours of unprotected sex, the efficacy rate is 61%.
plan B® has no long-term effect on your menstrual cycle.Most women will get their next period when expected, and their cycle will continue as normal. For some women, their period can come earlier or later than usual and be lighter or heavier. If your period is delayed more than a week, or if you have any other cause for concern, contact your healthcare professional. More than occasional use (more than once within a menstrual cycle or more than once a month) may impact your menstrual cycle. You may also experience a few days of spotting after taking plan B®, which is normal.
planb.ca/faq.html -- website with more info