I have a lump under the skin on my buttocks near my rectum. what could this be?

Multiple causes : Lumps under the skin in this location can be a number of different things. Epidermal cysts, pilonidal cysts, lipomas, and abscesses are common lesions found in this area. There are also other more rare possibilities. See a dermatologist or plastic surgeon to have the area evaluated for possible removal by excision.

It could be a cyst,: Abscess, lymph node etc. See your dr for reassurance.