Depo Shot

Ok so like 3 years ago I was on the depo shot for only 3 months because I did not like how it was making my body feel, since then I have not used any birth control and our only method used is withdrawing. Is it possible I am sterile because of depo, there has been quite a few times he has came inside me and I did not get pregnant. I'm not trying to get pregnant, just worried I will never be able to have kids. I am 21, not trying... But not preventing either.