How do i improve my sensitivity to anal?

I'm not sure if it's just that everyone's body takes it differently, but every time my SO and i try anal it hurts extremely bad that i just have to stop it at the beginning. Is there anything i can do to make it much more easier? I hate the fact that it has to be something i have to avoid because of the pain of anything in that area. Hope there's more things out there for me to do!.. Thanks for your time!:)