Oh and PS. I don't have the most hairless butt in the world, so does that increase chances of pilonidal cyst? I guess you need to have enough hair for there to be an ingrown hair and therefore a cyst?
But for me, the discomfort isn't right below the tailbone, it's much further down in the "crease" between the buttocks, with most discomfort being from just behind the anus to about halfway between the tailbone and the anus.
So, I guess it's most likely a fissure still?