(Concern) Skin itching

It seems that only one side of the upper part of my shoulder blade has been itchy for a few months. I tried applying dermatological ointments, and it improved temporarily, but then it itched again after a while. I thought it might be a keto rash because I eat fewer carbohydrates, but I don't know if eating carbohydrates makes it better. When I do cold compresses, it’s okay for a while... but if I scratch it, a red rash appears, and later brown stains develop.

Last winter, I caught COVID and couldn't eat much at that time, so maybe my immunity has weakened because of it... What could be the cause?