It’s a fungal invasion. It may also be in your digestive tract. The hard stuff is like super glue. It’s a biofilm. Possibly having more than one pathogen within the biofilm.
You said you went to two doctors and a specialist. Have you gone to a dermatologist? If you have a hard, cement-like patch on your head, unless you actually refused to show it to the doctor, it's hard to understand why someone hasn't been able to give you a diagnosis.