Pain & Muscle weakness and tiredness?

I am having pain and weakness in my right arm. It all started 2 years back when I was doing shoulder workout. The pain starts from the collar bone, trapezius, goes near the ears and the side of the head. it rotates down to the arm, deltoid and forearm. I cannot lift my arm without any support for more than 2 minutes. it feels like i my muscles are getting tired. I have gone to many doctors but they are not able to diagnose my problem. please help me out.