The causes of having a dry and flaky scalp are commonly seborrhoeic dermatitis or scalp psoriasis. These are both chronic conditions and require follow ups. Don’t worry, it is not infectious but need to be kept in control so as the flakiness is prevented. I would suggest you show your dermatologist again and perhaps he/she might modify the previous treatment taken. There are excellent formulations available in the market and the lead to good control of the condition. All the best