If you had [unprotected sex](https://www.bedsider.org/features/95) within the last five days, you might want to use emergency contraception. You can get [Plan B One-Step over the counter without a prescription] (http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm358082.htm). You can also look into getting a Paragard IUD, the most effective emergency contraceptive option.
If it's been more than five days, you can get a pregnancy test or go to the doctor to see if you are, in fact, pregnant. You have to wait at least 10 days after unprotected sex for the tests to work, and they are more accurate if you wait to take them until a few days after you expect your next period. If you're not pregnant, talk to your doctor about preventing future instances of unprotected sex.