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1.The possible cause could be an infected collection /
abscess - if it is painful on touch and tenderness.
2.Other possible cause could be
lymph nodal enlargement - which general after any infection, but less chances to get pain.
3.Other causes will be glandular masses,
lipomas.
4.For a definitive diagnosis get an
ultrasound neck done - that will help to assess the nature of the lesion, its source and extensions ( where all its extending)
5.Only after that a treatment can be indicated. In case of infected causes - a course of antibiotic will be helpful. Good luck.
Hope it helps you. Wish you a good health.
Anything to ask ? do not hesitate. Thank you.