I have been getting 1 painful sore on my butt cheek going on 4 yrs now. It will only come on one side. It is flat, and I ve been told it looks like shingles, but I only get one. It itches at first, but then it is extremely painful, and last about 2 weeks. No one has been able to diagnose me. There is never any fluid, so they can t culture it. What could this possibly be?