Hi.. Thanks for the query.. It seems that pain and lump on right lower butt cheek that discharges thick pus seems most probably be due to formation of a Perianal abscess It occurs most commonly due to hair follicle infection while other causes can be infected gland in the area or infection in the skin leading to pus formation under the skin.. I would suggest you to consult an Emergency room and get evaluated. He can advise you a course of antibiotics, anti inflammatory painkiller and topical application of antibiotic, steroid and numbing ointment.. Do warm compresses as it can ease in draining it off.. If it does not improve or start worsening then Incision and Drainage can help in faster resolution.. Hope this helps.. Regards.