What Causes Pain In The Arms Muscles?

I have constant muscle soreness in the large muscles of my arms and my lower torso. I am being treated with cymbalta and with norco 10/325 every six hours. They do make it bearable but not to the point that I can even do housework. The soreness makes me stiff so that I walk awkwardly. I also have advanced arthritis in both hands and some in my shoulders. Exercise helps somewhat, but too much makes my symptoms worse. The pain sometimes lessens, but it never goes away so that I am pretty miserable most of the time unless I lie down. Is there any clinic to which I could go for help? I love my doctor but he has not helped me much. I am 77 and have been extremely active all my life until about three years ago. Help!