What Can Cause Dandruff And Itching On Scalp?

Hi. For the past several years I have had a dandruff problem. It has only gotten worse recently. My head intches all the time. There is tons of dandruff everywhere. I have tried head and shoulders, some ayurvedic oils....!!!! Nothing works. Now some part of my scalp has change of colour and sever skin lose from those areas. Any advice????