@Rose000,
1) Pregnancy tests are cheap and easy to get and use. Get one. Follow its instructions TO THE LETTER. Usually, they tell you to wait until your period is 2 weeks late.
Whatever the instructions tell you to do, do them. You want to assure as much accuracy as possible.
2) A guy doesn't have to ejaculate in order to have what people colloquially refer to as precum. Can you get pregnant from it?
It's possible but rare. See:
http://americanpregnancy.org/getting-pregnant/can-you-get-pregnant-with-precum/
3) Withdrawal is a lousy form of birth control. Don't rely on it anyone, EVER. Instead,
buy condoms and use them. And go to your doctor and ask them about birth control, even if you are underage and even if your parents would object. You have the right to medical privacy even if you are under 18. There is no harm in asking at all. Ask about condom types as well. Your doctor can help you with that. Condom use is a good practice to get into because it also helps to prevent STDs.
4) Seriously consider (assuming your folks are not abusive) talking to your parents about you becoming sexually active. Yeah, it's not going to be a fun conversation. However,
it will help to cover you if your parents find condoms in your room or if at some future date, you end up pregnant and are still living under their roof.
5) And finally,
if you can't talk to your parents about sexual activity, and you can't talk to your boyfriend about using birth control, then you're probably not really ready for sex. So what do you do if you're frustrated and 'need pleasure'? There is masturbation, with or without a partner. There's also oral sex (although be aware there are ways to get STDs that way).
You can also relieve your stress in other ways, like getting enough exercise (with your clothes on) and trying to reduce school stress by working with a tutor or any other thing which might help your schoolwork to become less difficult.
Pregnancy scares stink but they are AWESOME learning opportunities.
Please be sure to learn from this one, okay?