I'm so sorry to just be getting to your message. At this point it's too late for you to use Plan B. You're old enough to have taken it.
Please know that Plan B is not a form of birth control. You can not use it every time you have unprotected sex.
I recommend you or your boyfriend buy condoms and use them every single time you have sex. Or, you can go to any woman's clinic to get on the pill, get the 3 month shot, the implants, there's even a 5 year IUD you can get.
At this point all you can do is wait for your period and if it's late them take a pregnancy test. I hope everything works out for you. I'm here if you have any questions.