Let’s start from the beginning. When you take your brand new puppy from the kennel, he might suffer from stress, but if you feed him with the same food and on the same feeding shcedule that the breeder did, it’ll probably make the situation a bit better.
For puppies under 4 months it is recommended to feed 3-4 times a day, but it is good to keep feeding them 2 times a day, even when they are adults.
You should pay attention to your GSD’s coat too: that is were you can see if the diet is not the best. If you notice hair loss or poor coat quality, chances are high that he’s not getting all he needs at his recent diet.