Hi... As doctor suggested it could be a pain radiating down from neck...
It could be a facet joint irritation or a disc issue that is irritating the nerve..
It could also due to chest muscle which could give u similar symptoms..
I recommend you to kindly do frequent icing for your neck and shoulder and chest muscle..especially in the area below the collar bone..
Frequent neck stretches and pectoral (chest muscle) stretches will help us to improve faster..
Next Steps
i suggest you to get a ecg done and consult a physician..
Health Tips
Do not lie on the affected shoulder..
do not lift and push with your left arm..