He is probably still traumatized and scared because of the surgical operation, which can be very painful, expecially when the anesthesia's effect fades and the wound is still open. My cat spent a time quite similar to yours. Just give him time, being understanding and patient. I am sure he will...
Try very gently to return the bite. Usually it is the mother which instructs her kittens to moderate their 'feline' side, but in this case you need to replace her! There is also to take in account the fact that the kitten is probably changing the teeth, and this can be a fastidious process...
Acana and Orijen are very high in proteic percentage, if the cat is not old, active and free from renal problems they are very good grain-free brands. Moreover, they are guaranteed as 'cruelty-free' (not tested on animals). Other very good grain-free products are Farmina and Granatapet .
Hypertiroidism could be another cause for overeating, but the cat should be thin and I suppose that the vet has already controlled if this problem is present.
Maybe he is looking for some nutrients he is not able to absorb from the food...this can happen even when a meal is complete and not complementary, He might need an integration which at the moment cannot still be defined.