What Causes Backache And Shoulder Pain?

I have been having pain in my back, right at the bottom of my shoulder, but more toward the center of back. It s a sharp pain, really starts bad while at work. Now I am having some serious pain in my left shoulder, right in the joint area. I can t extend my arm out completely with out it killing me. It hurts to hold my arm above my head, example washing hair, sleeping. Also in my left hand I have the most ungodly aches in my thumb. It hurts to hold things that requires my thumb to help hold. I can not put any pressure on it, and it comes along with pain that shoot up to my elbow. What can this be? Please help.