How to cum?

My boyfriend and I have been dating for 3 years and I don't know if I ever came. I've peed during sex like twice from him rubbing me but idk if that is it. He's always horny and I enjoy it but only in the beginning and then gets boring. We always do missionary and he's on top because I get tired easily being on top. I want to crave having sex with him like he does. What can I do or we do to make it better?