Pain during sex, it is my cervix?

Rachel • I`m 20. Been with my SO for 4 years!
Sometime when my boyfriend and I have sex, it feels like he's hitting a dead end and it hurts so bad! Is it my cervix? Usually when he's behind me it hurts the most. I don't no if it's my cervix he's bumping into or if I have a problem! Does anyone else have this problem ?