I had pain in my right shoulder for a few years, so severe that some days I couldn't raise my arm higher than horizontal. I eventually figured out it was because my mouse pad was way off to the right, and that was because of the number pad on the right side of the keyboard taking up so much real estate on the desk. So after trying a couple of different mouse alternatives, like a roller bar, etc. I got on Amazon and bought a keyboard without a number pad, which moved my right arm inward, and pretty much immediately ended the pain.