How do you tell if you're fertile?

Okay so my boyfriend is super fertile and I know that you can get pregnant at any time. I also know that pulling out still has the chance of conception. I don't know if I am fertile? Like at all. I've had a lot of sex and most of it unprotected but I have never gotten pregnant. I'm scared because we're both super young and I don't want to drag him down with a kid if I do get pregnant from all the sex we've been having.