Hello,
Welcome to the ehealthforum and I am really glad to help you out. Your concern is regarding the lump that you are having on your buttocks cheeks. This kind of lump can be a sebaceous cyst or a benign growth of the skin. Cyst is a closed sac or cyst below the surface of the skin that is usually painless but can become painful if infected.
What exactly is this can be diagnosed only after examination and investigations like ultrasound or CT of the area. Till that time you can apply warm compresses.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care.