I have what feels like a strain running from behind/under my left shoulder blade, running across the outer part of my left deltoid and creating a aching throbbing pain in my left forearm on what feels to be right in between the two bones. I do condition with weights and it has been this way for about two weeks. I do have strength and motion forward, outward, inward but the shoulder press and incline press going upward do have a drop in strength. There isn't any sharp pain aside from the aching and throbbing. Any way to confirm if a nerve, tendinitis and or treatment?