Dear Friend, The real reason for the pain may be in the neck and not in arm. Are you a IT professional? or do you work on computers for long times? As such pains are very common in IT  or computer professionals. It is because of improper posture during long working hours that causes weakness of muscle of neck, back resulting mal alignment of vertebras. This results in compression of nerves that reflects as kind of pain that you have. Please get a Xray of your neck done and see a doctor. Best wishes.