There are a number of skin conditions that can behave the way you describe, like scabies,
eczema, psoriasis, pityriasis lichenoides and many others. I recommend a consultation with a board certified dermatologist for proper diagnosis and treatment.
Scabies, an infestation with a mite, Sarcoptes scabii, for example, is very itchy, looks like small red bumps with a linear scale (burrow), can spread all over and often involves hands, feet, underarms, waistline, genital area.