What Causes Severe Pain In Left Shoulder Area And Breathlessness?

Hi, I have been having pain running from my left shoulder blade toward my spine around to my left pectoral area for a few days now. Certain ways I move my left shoulder causes debilitating pain. I have asthma so I really am not sure if the shortness of breath is from the asthma. It hurts to take a deep breath and I feel like I can't get the air I need at times. I haven't done any heavy lifting. The closer I keep my left arm tucked in and immobile seems to lesson the discomfort.