I have a large swollen painful bump on my butt cheek it's in the crease of the bottom of my rear and leg i can't sit have any idea what it might be ?

Possible abcess: Sounds like you may have developed an abcess (a collection of pus/infection) in that area. If this is the case, you need tobee seen by a medical professional who can see if the pus needs to be drained out and possibly antibiotics. This should not get put off as these things can get very bad and the infection can spread, including into your body.