What happens when sperm enters your body and then you take the birth control pill?

You don't say, but I'm going to assume you're a girly.

So you had sex unprotected, and you're wondering if taking the pill after you had sex will stop you getting pregnant. Sorry, its a bit late if its been less than 36 hours, get straight to the doctors, and ask for a morning after pill, so you can be sure.

Now if you're old enough to be having sex, surely you're old enough to get hold of some proper contraception, and make sure this doesn't happen again?