Did you use any form of protection? If not, you can use an emergency birth control pill (the morning after pill) up to 72 hours after intercourse. The sooner you take it, the better. I'm not sure of your age, but you can get it over the counter at a pharmacy if you are over 18. The morning after pill (plan B, etc, etc) are good to use when you don't use protection, or otherwise your protection fails (you miss a birth control pill, your condom breaks, etc).
I can't tell you whether or not you are pregnant. If you've already had sex, then there's nothing we can do at this point (other than the morning after pill) to change anything that might happen. Remember, you have 72 hours (sometimes more) to take that pill, the sooner, the more effective.
Now, a few things. A pregnancy test can be taken as early as five days before your expected period. However, women differ from one another, and if you take the test early, the results may not be accurate. In your case, I would wait until 2-3 days after you expect your period to have come. Remember, if you are stressed out or worried, your period can easily become irregular (you can even skip one!). So that's another thing to keep in mind. Likewise, if you're ~worried~ that you're pregnant, you're going to start noticing 'symptoms', that really aren't there.
Do your best to stay relaxed, and don't jump to any conclusions until you know for sure what's happening in your body. From this point on, if you plan to continue having sex, do so carefully. Take the proper steps to ensure safe sex. A condom is the only birth control that can protect against STDs, and there are many other methods to use, which you can talk to a gynecologist about if you are interested. It's better safe than sorry, and the extra money is much cheaper than raising a chilld, or even the cost for an abortion.
Try and stay calm, nothing is for sure yet. You can look at an ovulation calendar (Which you can easily find online) and figure out when you are most fertile. This may help ease your mind, and can help you understand a bit more about your body as well. Just another thing that you may want to look in to.
I wish I could help you more, I tried to cover different areas. If you do take a pregnancy test and it does come out positive, make sure you go and talk to your doctor to verify the results. The doctor will also be able to help you decide what is the best path for you to take, and will tell you all your options.
Best of luck.