What should i do if i have a boil about golf ball size on the bottom left side of my butt cheek with no head and has been their for a week & hurts?

Boil/abscess: Boils/abscesses are common i the buttock area and can be painful. They often will need to be incised and drained (i&d'd) to be treated most effectively. Antibiotics and warm compresses will help before you get it i&d'd and may even "bring it to a head." but you best advice is to let a dr. See it and get it properly treated with i&d. Best wishes.