Burning sensation in upper arm with shoulder blade discomfort. started a couple months ago pretty sure from a work out ?

Muscular injury: If this is still persistent this long this merits orthopedic consult. It may be a muscle tear or strain. Have you rested it.? Take time and see the doc.

Neck: Have your doctor check for a pinched nerve or herniated disc in your neck. Another possible cause could be rotator cuff tear in the shoulder. You should see your doctor for an evaluation. Good Luck