Confused..

My fiancé and I have been together for about 2 years now. We've talked about having a baby, but not really TTC, hoping it'll just happen.. Because every time we've had sex, it's been unprotected and he ejaculated inside, everytime. Yet two years later and I'm not pregnant.. My periods are never regular. I thought I had experienced implantation bleeding a few months back, but tests were always negative. Would anyone have an idea why? Is my body just not made to have babies? Is it his sperm? Just possible ideas would help my wandering mind.