Sex and other things

Me and my boyfriend have always had unprotected sex, and he always got to cum in me. We did this over a year, and I have never gotten pregnant. We've had times were we thought I was, but it was just my period on the way. It scares me, because I don't know if this means my chance of kids doesn't exist. And I'm 17 almost 18 and absolutely can't ask my mom to take me to a doctor. Any thoughts about this?