What Causes Itchy And Burning Rashes On Skin?

i get an EXTREMELY itchy and almost burning rash that comes and goes. it seems to appear symmetrically in my body- on the tops of both feet or on the inside of my legs near both knees. it appears to have puss underneath. i have never had an intense itch like this and usually scratch it unti a few of the little bumps break, then they scab...