hi. noted history of recurrent lump containing smelly pus. based from your description, it may be a case of a recurrent cyst formation (sebaceous or keratinous type). it is best if you consult with a doctor, preferably a general surgeon, for physical examination and clinical evaluation. definitive management is surgical excision of the lesion (complete cystic excision, including the wall, to decrease the risk of recurrence). antibiotic treatment will be prescribed accordingly along with daily wound care after operation. hope this helps. good day!! ~dr.kaye