Okay, So Me And My Boyfriend Were Messing Around A

Okay, so me and my boyfriend were messing around a tiny bit. I've never had sex at all, I'm only 18. I don't even feel comfortable being a girl. Anyway he was just rubbing against my butt, and he said there wasn't any precum a part from on my butt cheek, but he was against my butt hole a couple times and might of nudged the very edge of the other hole, I stopped him after that. He didn't cum but I'm still worried. I've had my period (I think) it's lasted three days and stopped the 4th day morning, I read that you can still get a period like thing while pregnant. I don't think I've shown any signs either. The only thing is ihave a bad cold, twice. Once when we did that, and it kept going, then when I wad finally getting better it got worse again! It's been three weeks now. What are the chances of me being pregnant?