Why can't I sit on the floor chair or car without extreme pain in my left BUTT bone or cheek it hurts to even walk and have throbbing pain sitting all day?

If you are having trouble with your hipbones after sitting on the floor, the best thing to do is invest in some chairs or at least a cushion; floors aren't made for sitting on, and it is unnatural for people to sit on hard substances (concrete floor panels, solid wooden planks, etc.).