Buy a home pregnancy test, if it's positive - go to the doctor. If he says you're pregnant, then you can start stressing out.
I managed to get pregnant at the age of 17, and it's not the end of the world, but I had an abortion so what do I know. It was with a random guy who wanted nothing to do with me. You got any friends you can turn to? If you have a decent relationship with your mom I suggest you talk to her.

And if your boyfriend isn't supporting you, honey - don't waste your time on him.

About abortion vs keeping it (NO I don't want to start a debate!), I encourage you to make a choice that you feel will be the best for the potential child - and not base it on whatever values or morals you may have; that would be selfish.
When I found out that I was pregnant, the first thing that popped into my head was "I'm 17, I'm single, I'm in high school, I don't have a job, I'm bipolar... there is no way that I can take care of a child at this point - I will not force a child to life if I'll be unable to take care of it. I'm not that selfish".

You've got plenty of time to think it through, but I hope that you DO think about it and not just say "I'm gonna abort/keep it because that's what my morals tell me is right".

If you got any questions or just want to talk about it, please don't hesitate to PM me.