What Causes Pain After Sex In Left Side Of Buttocks?

Hi, I am having a constant pain in my left bum cheek, like it is all bruised, and it is constantly aching, laterly sex has been really painfull, (I've never had this issue before) but for the last 6 month it's very painfull, to the point I don't really want it anymore and I haven't sorry to be rude had an orgasm since this pain started. When I'm due on the pain gets worse and my back on the right hand side and bum cheeky is in agony! All my leg and arms on the right hand side feel like I'm buries when touched!