Muscle strain from using the mouse

How common is it to strain your muscles especially on your right side from using the mouse all day? Do you ever injury not the shoulders but the muscles on your sides next to your ribs? Have it ever gotten bad enough that it hurts to breathe heavily?

I am having this issue and I am not sure if it is related to me using the mouse with my right arm stretched too far forward. If these sort of strains are common, does anyone have any advice to avoid it in the future?