Need help? May be pregnant?

I had unprotected sex with my boyfriend a little over three weeks ago, it was my first time and lasted only maybe two minutes because he didn't have a condom and I know for a fact that he didn't *** but I've read about pre-*** and everything so I'm still skeptical. My periods always start around the fourteenth of every month and mine started a few days after the fourteen..they're also always remotely heavy and right now it's extremely light. I haven't taken a pregnancy test yet, but I plan on doing that. I'm just not sure if I sure worry or not about this.