What Causes Hardening Of Muscles And Pain?

I have hardening of my muscles and have been tested for all the normal stuff. I look almost like a body builder and I don't (can't) do anything that would harden my muscles. I stay a lots of pain all the time. I have lost my job from it because my doctor will not release me to go to work. I need to know what this is and how to treat it. Does anyone have any ideals?