Really need help with this one. no hate.

I'm only 16. However I have been with my boyfriend for 3 years and have been having unprotected sex for around 1 and a half - 2 years so from the age of 14. Yes not sensible at all at that age but pregnancy has never bothered me and if I did get pregnant I would have actually been happy. But the thing is I've never gotten pregnant and because it's now one of my main goals in life when I'm older its worrying me. I know I shouldn't be worrying about this now but it really is a dream of mine to have my own family, I'm not saying I want to get pregnant now but I absolutely do want to when I'm atleast 20. I can't help thinking I'll never be able to have kids I just find it crazy how I'm young, healthy, been having unprotected sex for that long and have never gotten pregnant when I know so so many girls that are younger than me and have already had a baby.😮 Has anyone got any suggestions to why? Could their be something wrong with me? Is it possible that its because my body hasn't fully developed yet? I know I'm young but I'm so curious!