I had a large lump on the inside of my butt cheek and when i sat down today it busted open. a bloody puss type of fluid came out what could it be?

Butt problem: You had an abscess on your butt which popped and drained. Take care of yourself and hopefully this will not recur.

Pilonidal cyst: A pilonidal cyst is an abnormal pocket originating in the skin that usually contains hair, skin debris and other abnormal tissue. A pilonidal cyst is almost always located near the tailbone at the top of the cleft of the buttocks. The only sure treatment for a pilonidal cyst is surgery.