I'm Never Going to Get Pregnant

Why is it when two people are just fooling around they get pregnant but the people who actually try don't? It makes me so mad and upset and honestly I feel like it's never going to happen to me. I'm healthy. Young. And sexually active with only one person. People I know have gotten pregnant when they weren't trying to. But the moment someone who actually wants it, they don't get it. I almost want to go and get myself checked out to make sure I'm even able to :(