Pain that gets worse with deep breath may be caused by a respiratory or chest wall problem.Possibly a strain in muscle and ligaments od chest wall.
But at your age a precautionary ECG can be done to rule out any cardiac cause.
It is usually caused by coughing ,exertion,injury but some times can occur spontaneously.
Well since this is radiating between shoulder blades i would recommend an ECG to be on safer side.
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