Parvo is quite devastating to the gut lining. It quite often kills
young puppies, and indeed adult
dogs. So your pup is at an advantage already
in that he has survived.
Fighting this takes a LOT out of the immune system too. Your little pup then got a dose of kennel cough when he was at his weakest. Poor little thing.
He needs to heal and fully recover and this takes quite a while for the gut lining to heal and for him to tolerate food.