There are urgent contraception-pills that are called "emergency pills" or "Plan B" pills that you might be able to take to prevent an unwated pregnancy. However, these birth control pills should be taken (at most) 72 hours after intercourse or unprotected sex. Having unprotected sex a few days before the period should be relatively safe ... if your menstrual cycle is regular but you can never be 100% sure. If your period is late, you can take a home pregnancy test to check if you are pregnant or not. And then you can follow up with a gynecologist if necessary.