I have anxiety issues about pregnancy. HELP ME PLEASE!?

Alright, i know this gonna sound stupid, inmature and ridiculous, but i really need help. I started having sex with my gf about 3 weeks ago. It was the first time both of us have sex ever, (we are both 19) however after last time we had sex (this weekend) i got the idea of pregnancy stuck in my head! Every single time we had sex i used a condom, and pulled out! However, for some reason my mind is obsessed going over the details of what we did, thinking that i might had made some mistake that could have gotten her pregnant! (maybe precum slipping in some way while touching eachother??? even though i am extra carefull with that kind of stuff) this is a nightmare, but i don't wanna talk about it with her because it was already very hard to get her to have something with me, and i don't wanna scare her... or look like an idiot.. I want to talk her into taking the pill so i can be more relaxed... idk, i just wanna have a normal sex life as any other teenager... =( it's just annoying my mind is such a *****... and my boddy is taking the toll for it, i even feel sick right now.. WHAT CAN I DO TO CALM DOWN??