Brief Answer:
I won't be worried if there is only swelling and pain

Detailed Answer:
Hello

Thanks for the query

I would like to know-
By sore,do you mean there is an ulcer or just there is swelling and pain?
Is it on one side or both side?
For how many days it is there?
If there is only swelling and pain then first I would like to rule out pubertal gynecomastia.
This is a common condition in puberty and no specific treatment is needed.It usually subsides on its own.
But if there is an ulcer then this may be due to mastitis.
Mastitis needs to be treated with local and or systemic antibiotic.Even sometimes surgical intervention may be needed.
There can be some other uncommon causes also.
I would like to get him evaluated by a pediatrician for clinical examination and management accordingly.
Waiting for your reply
I shall be glad to answer if there is any more query
Regards

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