Help me, pls

Hi

Sorry to be such a nuisance, but not only is my bird now underweight, and unhappy, but when I got back from work yesterday, I found that he has damaged all the feathers on the top of his head. It looks as if the feather have been broken off and now he's almost bald on the top except for a stubble like look where the feathers have broken off. What is going on with my "Boy" is this because of the drastic changes to his diet that we have been conversing about, or is there another problem i don't know about. This damage is about 2mm from the top of his beak almost from eye to eye on the top of his head. I am so sorry i listened to an avarian vet regarding the health of this bird, i should have just stuck to my intuition