Scalp dermatitis? Flakey skin, big flakes, yellow, scalp-like scab texture. Spread to scrotum, wrists, knees, elbows, bleed when combing, hard to comb

Spreading rash. The location and quality of rash sounds like you have an extensive case of psoriasis. You need tobeunderthe care of a dermatologist, prefably one affiliated with a teaching institution.