Have someone support your arms in a shoulder shrugged (passive scapular elevation) position (or rest your elbows on a table and sag down) but be sure you remain passive with upper traps relaxed. Turn your head in the painful direction. If it's not painful or you can turn your head significantly more than with your shoulders in normal posture, you most likely have a scapular stability issue. Stretching won't be the fix. It'll be an isolated weakness that needs to be resolved.
If it's the same regardless of passive scapular position, look more for a neck issue.
Bill
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