Infertility?

So when I was younger, 15-18 I had a boyfriend who i had sex with quite frequently, we didn’t use protection and we didn’t pull out. (We were young and stupid and thought we could handle kids), I never ended up getting pregnant. I have had 2 boyfriends since then and they have done the same thing and I’ve never gotten pregnant. Someone I have been sleeping with now for 6months does not pull out. I’ve never ever been on birth control. I haven’t gotten pregnant ever and idk I’m wondering if this seems abnormal that 3 men have came inside me and I’ve never gotten pregnant, I just see everyone around me having kids and getting pregnant, I’m curious why it hasn’t happened to me? (I’m almost 21 now btw)