Well, I use the human kind and have for many, many years. Are you using a metal comb? I hold the tangle with my fingers against the scalp so it won't pull and then comb it out gradually. It takes quite awhile for their hair to get long. If my memory serves me right, it was at about 8 months or so before the hair was long. But once it starts growing, it grows fast from then on...
As to food, I would ask what your puppy's age and weight are and whether his food was changed when you brought him home from what the breeder was feeding him. It helps to sit with the finicky one's, if they won't eat. I have found that they will eat with you there. I gather you are free feeding.