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Small and nodular lump in the neck and behind the ear are mostly due to swollen lymph
node unless proved otherwise. Presence of redness
and tenderness above the lump probably suggest the infection is localised above the area.
The short duration history of symptoms and the described condition sounds a benign condition, however it warrants a clinical examination. You may need a course of antibiotic for the time being. Further diagnostic and therapeutic procedure is entailed should the symptom worsen or if you develop fresh and severe symptoms.
Hope I answered your query.