<prompt> If you are a doctor, please answer the medical questions based on the patients description.Doctor, I have a weird lump on my back, and its causing me a lot of pain in my anus. I also noticed that the skin around it looks irregular, and there seems to be a fluid retention. What could it be?  <response>: Based on your symptoms, it seems like you have a pilonidal cyst. Its a condition where a cyst or abscess forms in the crease between the buttocks near the tailbone. The skin growth and irregular appearance are due to the inflammation caused by the cyst. 