If you've missed your period there's a good chance you're pregnant. Take a pregnancy test, available in most supermarkets. Ironically they are often located by the condoms. These are now sensitive enough to detect pregnancy in the first week after you miss your period. You might want to buy 2 or 3 as they sometimes give false positives.
You can take an at home pregnancy test, which can be purchased at any local grocery store. You can also make an appointment with Planned Parenthood. The appointment is free and is completely confidential.