From your description it looks like severe seborrhoeic dermatitis
based shampoo containing ZPTO is a good treatment. As this alone is not working for you, you should take an oral course of ketoconazole 200 mg once a day for one to two weeks. Ketoconazole 2%cream should be applied twice a day over the face rash
and continue using it. Get this prescribed by your doctor.
This is caused by a lipophilic yeast which loves oil. So do not apply oil over scalp
Hope this helped