Skin Condition on a Golden Retriever....?

[Harley]

My Golden named "Davidson" has some weird white residue in his undercoat and he is loosing a lot of hair, by the bundle. He gets every month his Frontline (for fleas, ticks, etc.) and Sentinel (for all the worms, etc.), I bath him every two months with a very gentle Oatmeal shampoo, and he gets brushed every second day. He looks unhappy which is so not him, he is a happy go lucky kind of a dog. Does anyone might know what that could be???? I have an appointment for him this coming Wednesday, but just wanted to know what other people might think of this.