you have a very unhappy bird. i dont know if he is by himself but he needs companionship,. cockateils are flock birds and a solitary one just doesnt know how to behave and has nothing to interact with. if you do not want another bird for some reason, put a mirror in with him. hanging toys that he can climb and chew on may divert him or may not. a cockatiel by himself is kind of like a person in solitary confinement in a small cell. find ways to divert his attention. putting bird vitamins in his water may help him when the new feathers try to grow but are not the answer to what he needs.