I can't have babies or can I?

Okay so I've been having unprotected sex with my fiancé and we both are some kinda of sexually active..when I first met him I never had my period but now I do. I get heavy period and sometime I get it light. But since the time we been together I just noticed that I'm never pregnant..which is weird....we've talked about it but right now may not be a problem but soon in the future it maybe ? Hope so?!