A baby shouldn't be losing feathers until his first molt at about 6 months old when his first adult feathers start coming in. I'd you have access to an avian vet you should bring him in for a developmental exam and to get professional advice on feeding and weaning. Weaning is a delicate process and baby birds are vulnerable to psychological harm and malnutrition if it's not done properly. Captive hand fed parrots tend to wean later than their wild cousins because parent birds teach them what and how to eat on their own, something we humans are not as well equipped to do.