You are probably not pregnant.
However, if you are still worried, go to a drug store and buy a home pregnancy test and follow the directions to the letter when you use it. That usually means waiting until 2 weeks after your period was expected. If you end up getting your period anyway, keep the test and use it in the future if you feel you need it (but do check the expiration date and toss it if it's expired). These tests are super-cheap these days, as in less than $20.
And make an appointment with your doctor. Or, if you are a minor and still living at home, ask your parents if you can see your pediatrician. Feign headaches if you must - getting to your doctor is more important than the truth right now. Go and ask for birth control and talk about pregnancy symptoms. Condoms are fine and they are a terrific start but you will decrease the odds of pregnancy even more if you are on the pill or using an IUD or other barrier method. And you will breathe a lot more easily if a medical professional answers your questions.
You can also go to Planned Parenthood if they are in your area. PP does a lot more than offer safe abortions. In fact, abortions are one of the least common things they provide. Get your boyfriend to take you if you do not have another means of getting there because he should be a part of this as well.
If you are old enough for sex, then you are old enough for a home pregnancy test and the act of buying one, you are old enough for the pill or another form of birth control, you are old enough to go to Planned Parenthood, and you sure as hell are old enough to talk to your doctor about sex.
And if you can't do any of those things I've listed, then you might want to rethink the whole idea of being mature enough for sex in the first place.