Bad dandruff problem, help?

I have bad dandruff, when I scratch it I can feel large chunks so I peel them off and they're about the size of a watermelon seed but flat and skin like.... uuhhh. They are visible in the mirror and most have blood underneath and around it. I even have some next to my winky above my . I use Head and Shoulders everyday but like within the day it comes back. What else can I do to stop this YO