3 Week Pregnancy?

So my boyfriend and I have had unprotected sex quite a few times. I'm on birth control, but I know that that's not something to completely rely on. My last period was the week of thanksgiving and I knew that my next one would be shortly after Christmas, but it hasn't happened. I've done the no-no and gone to the Internet and read up on my symptoms and I have everything that leads up with a 3 week pregnancy. I've heard of woman finding out that soon but I've had some spotting and I don't know if that means I'm supposed to start soon. What should I do?