Is your vet that you are using a board certified avian specialist? If not then I suggest making an appointment with one. If one is not available in your area then I suggest going outside your area. Your vet should have given you some solutions. I used to always think that behavior modification should always come first. Now I really think that its a mix of things. Quick question: how old was he when you brought him home? Did he come from a private breeder or pet store? Was he kept with other babies before you brought him home? How long have you had him? When did the behavior start? Have you talked to the breeder about what they think is going on?
I would suggest getting this problem under control as soon as you can. I would suggest letting his flight feathers grow in (any bird that is prone to pluck, shred etc. should NEVER have any physical alteration done i.e. wing clipping, or it will encourage the behavior). I would build an aviary outside. Until the flight feathers come and he is flying outside all day in the aviary, I would suggest having a collar put on. I would have the collar on until hes flying well and is adjusted to the aviary. Then I would put him on a med that calms him and have the collar removed. Once the collar is removed then I would slowly wean off of the meds. This process may take up to a year. The collar is not the fix to the solution, the collar just allows you to make adjustment and allow the feathers to grow in fully while those adjustments are being made. If the feather shaft gets damaged too much they may not come back or you will end up with cyst formation - which would have to be surgically remove.
However I am not convienced that there isn't anything else going on, maybe a food allergy, rare skin condition, communicable disease etc. I would go to a specialist, perhaps the state university or even the next state over. It is not normal for a baby to be showing this type of behavior and would def get a second and third opinion before taking the measures I listed above and I would do them sooner vs. later. There is obviously something going on. If you have three board certified avian specialist tell you that its nothing physically, then I would do what I mentioned above plus I would get an avian behaviorist involved, one that does home visits.