What Causes Warmth And Pain In Buttocks/tailbone Region?

My husband is experiencing a great deal of pain in his tailbone/buttock region. He has no recollection of falling on it or bumping it on anything. He can barely sit down without wincing. I looked at it and it has a slightly raised reddened area on his right cheek near his crack. It sort of felt warm when i touched it and he said it hurt pretty bad. I was thinking that since he didnt bump it, that maybe it is a spider bite or something like it, although i saw no actual bite mark. Any ideas?