What Could A Painful, Spreading Bump In My Butt Crack With Throbbing, Fever, Nausea, Headaches, And Lightheadedness Be?

I have a bump on my butt crack and it causes pain it feels like it’s moving or throbbing. I can’t sit down and lay on my back. It started in one spot and now it spread to like my whole upper crack. I feel nauseous sometimes I get headaches and lightheaded. And fevers only at night tho