What Causes Painful Blister In Between The Buttocks?

I have a tiny spot inside my butt cheek to the right that is very sore. I think it's a tiny cut. Its been kind of aching for a few weeks. It seems like it won't heal. It will even burn in the shower when water touches it as well. It's no sore, blister, or bump. Nothing like that. How can I cure this problem?