My hair has bad buildup (like dandruff) how can I get rid of this?

First of all, I'm very fair and have oily skin. Ever since I has in fifth grade I've had very bad "dandruff". Recently, my hair stylist said it was because I was using waxy shampoo. I switched to the more expensive brand she recommended, but it didn't help at all. My colourist said it was the type of water in my shower, but when I was younger I lived in a place with well water and it did the same thing. How can I stop it from happening?