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Apart from pain , do you have any other symptoms like burning sensation of stomach , belching , hyperacidity
? Did you have any trauma previously ?Do you have any neck pain
?Is there any discolouration or tingling sensation
of your arm ?
If you do not have any associated symptoms , it could be brachialgia , for which you should visit your Orthopedician and get examined.He may advise you the specific treatment and physiotherapy
if needed. You can provide these details as comment to this reply or feel free to ask me.