It's nearly impossible for me to have sex?

i've been with my boyfriend for 4 months now and he and i have tried having sex 3 times before and no matter how hard we try he can't seem to get it. it feels like my flesh is ripping i thought i was supposed to stretch?! i'm wet and everything, i love him we partake in foreplay beforehand and it's all done right but when he tries to enter me he can't get it at all we've tried practically pushing and at that point it hurts so bad i'm near to tears. Is this how it's always going to be? i really want to engage in this i mean maybe the setting isn't right? it's always been in the backseat and i'm probably paranoid in case of interruption should we just hold off till we can be completely alone and secure? btw we use protection so it's all good. help!!!