Scratch causes some kind of infection or growth of bacteria on buttocks

Hii doctors. I wanted to know if there is some dermatologist here. I have some kind of thing on my buttock where in winters it is not there and when monsoon starts with little scratch it comes back that thing really asks me to scratch it constantly till blood comes out and it is really irritating

The skin becomes scaled and that fungus or I don't know what just goes all over my buttock

What is it ?