I have a burning sensation under neath the left shoulder blade under my breast and down through my left arm. at times its difficult to lie on my back?

Possibilities: You might have notalgia paresthetica, but the full description points toward brachial plexus. If your symptoms increase on elevation of your arm, could be thoracic outlet syndrome. If better on raising arm, might be nerve pinching in neck.

Tough: Its likely musculoskeletal with spasm. Is it worse in the hand the goes up, it may be carpal tunnel but it sounds kind of like an injury. Nerve pain is called radiculopathy and u may need 2 consider getting seen. Clinching or bringing teeth at night is often overlooked and not sleeping well delays healing but you may need 2 get seen. Good luck, try 2 aleve (naproxen) 2 x per day in the meantime ifapplicab.