HEAVY DANDRUFFF!!! someone help :)?

Hey guys, I’ve had dandruff for over 3 years now, and it’s very irriating, when i scratch my head, there are literally 100s of flakes on the ground. I’ve tried heaps of methods to cure it, but it doesn’t seem to have much effect. I went to the doctors and she just said use nitrozel or w/e it was. It didnt help at all… someone help