This sounds like a case of seborrheic dermatitis.
Seborrheic dermatitis presents as greasy and yellowish scales on
the body. This may involve areas
of the face, chest, and scalp. Definite cause for seborrheic dermatitis is not known. Yeast infections have been associated with this. I would suggest that you continue with your medicated shampoos. There is really no definite treatment for seborrheic dermatitis. If the condition is severe, topical corticosteroids may be able to help.