Agree 100% with Factorymomma- take a test and USE PROTECTION next time. You want to enjoy the rest of your teenage years, not be a mom.
If you're having unprotected sex, you can get pregnant.
That said, tons of things can make your period late even if you're notoriously regular.
Things like: stress, illness, diet change, exercise increase (or decrease), change of meds you may be taking, or sometimes it's late to just be late.
What you need to do is take a home pregnancy test with your first mornings urine. This is when the pregnancy hormone is most concentrated.
If negative, wait a week and test again if no period occurs.
If negative again, I would go ahead and call your ob and explain your situation and request a blood test. it is the most sensitive and will tell you definitively if you are or are not.
Just remember condoms and birth control cost a LOT less than diapers. Just fyi...