HI.Dandruff is often a long term issue; sometimes when severe, its better you see a qualified dermatologist to rule out presence of scalp psoriasis, which some people mistake as dandruff.
Rx . 1. You may need antifungal based shampoos for a few months.
2. avoid using any kind of oils in your scalp.
Next Steps
SEE A QUALIFIED DERMATOLOGIST NEAR YOU