Dandruff is a common situation more common among teenagers. It can be more problematic if you are using hair oils. So consider discontinuation of oils and using an antifungal shampoo everyday for first week and then reduce the application to twice a week for maintenance. You should keep the shampoo at-least for 5 minutes on the scalp for it to act. This should solve your problem. However if problem persists, consult a Dermatologist for proper diagnosis and treatment and to rule out any other skin condition. Hope it helps you.
Your dermatologist will decide a treatment plan for you after a consultation.