Hello, As per my clinical experience, the lump inside the right buttock with soreness on touch and difficulty in sitting indicates possible sebaceous cyst with infection. As there is underlying inflammation or collection which is responsible for stretching of overlying capsule of the lump and impinge on nerve endings which carry pain sensation to spinal cord level. Though primary relief with analgesic and anti inflammatory molecules, a better precision guidelines can be figured out with the help of a high resolution photo image of the lump during follow up discussion. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Bhagyesh V. Patel, General Surgeon