It is a bit too early for you to be having symptoms. If your period isn't due for three weeks, and you had unprotected sex a week ago, you have a lower chance of pregnancy. (I'm guessing you had sex right after your last period) But it just lowers the chance ( assuming you didn't ovulate early) and doesn't mean you couldn't still be pregnant.
I know this isn't what you want to hear, but using the "pull out" method is how I got pregnant. We only had sex one time that month, and poof! I learned my lesson, and have been EXTRA careful ever since.
I hope everything works out for you!