Conceiving after years? Is it Possible?

I'm 20 years old and have been having unprotected sex with my boyfriend since I was 16. I've never gotten pregnant. We were never sure if it was him or me, and were never trying to get pregnant. We just assumed it was never going to happen. 
​I'm 2 weeks late now and I have regular periods.  I know It takes a while to get pregnant. But 4 years?? 
​Just want to know mother's opinions, if I'm not alone. Has this happened to anyone else?
​I'm waiting another week and taking a pregnancy test 
​Thanks ?