What Causes Rash On Hip And Sore Patches On Buttocks?

I have got a rash on my right hip that feels exactly like sunburn. It blistered with hundreds of small blisters and the skin is now peeling. I simply woke up with it a few days ago. This is the second time in about eight months. I have other sore patches on mu buttocks as well but not as bad as the main patch on my hip, any ideas?