Brief Answer:
Costochondritis or mastitis.

Detailed Answer:
Hi.
Thanks for your query, albeit short and specific.
Since you have got tenderness in one breast since one week after getting chest cold, the most probable reasons can be as follows:
There may be costochondritis underneath the breast that can cause such pain that increases on movement of the body and on coughing.
Can be mastitis that is inflammation of the breast tissues.

I would advise you the following in such a situation:
Use breast support.
Take an anti-inflammatory with painkiller property like Ibuprofen if it suits you.
It is highly advisable to go for Ultrasonography of the breast as it may give a better diagnosis.

I hope this answer helps you.
Please feel free to ask for further relevant queries if you feel that there is a gap of communication.

Please give additional information for me to assist you better:
Is there any localized swelling or area of tenderness?
Is there any change in skin color?
Any fever, chills?
Any other symptoms or information that you would like to share?

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