Scalp infection can be caused by some bacteria or it may be fungal(tinea capitis). Sometimes what appears to you as dandruff can also be eczema scalp or scalp psoriasis. In these conditions, skin elsewhere in body may also be affected. You need to get your scalp examined by a doctor to get accurate diagnosis and get treated accordingly. Early diagnosis and treatment will help you prevent further damage to your scalp and hair.
Next Steps
apply any oil 1 hr before hair wash and not after hairwash, keep your scalp clean, protect your head from dust and too much sun exposure. Stay hydrated and take healthy diet rich in proteins and vitamins.