Thanks for all these additional details.
I can understand your concern.
Well, this could be related with a growing infected Cyst.
Other possibility is- Cellulitis (infection of the skin and associated tissues).
It can also be growing nodule which has became inflamed.
The pain indicates an inflammation, or an infection.
You need a clinical examination and tests for precise diagnosis.
Alternatively it can be an abscess in the early stage.
Your doctor may drain it or perform surgery to remove it.
Surgical removal may be done if the lump is especially painful or problematic.
This should not be left ignored.
I would recommend that you visit your primary doctor for clinical evaluation and get it managed.
Hope this helped
If you have any further question then you can ask me.
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