Hi, I Have A Lump Located On My Left Buttocks

Hi, I have a lump located on my left buttocks , not near the anus but moreso on the cheek itself. It's very hard and painful. I've used hydrocortisone cream, which doesn't seem to be working. I sat in a bathtub also but it only worked temporarily. I dont know what else to do. Anything as to what this might be doc ?