feeding, Poop, & Imunizations

Question
I have a 8 week old German Shepard puppy who is currently eating Purina puppy chow, how much food or water should he be eating at this time.  He was given his first series of shots today and his poop is a bit runny.  Should I change his diet or is this typical for a puppy.  He has only been with me 4 days and the first two days it seemed normal.  The last two days it seems to be getting runnier.  
Please Help!  
Thanks in advance,
Belyndia  

Answer
Hello and thank you for your questions,

It seems normal for a bit of runny poop after a vaccine but I've not noticed it with any of my dogs. Purina puppy chow had caujsed my labrador retreiver to have runnier stools then she has now as I fed it when she was a puppy now all my dogs are on Authority avalible only at petsmart stores. Changing to a higher quaility food may help runny poop and he will technicly eat less and poop less as more nutrance is derived from the food at once. Pruina puppy chow states the amount to be fed daily for a puppy according to weight check out the chart and feed it accordingly.