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					Originally Posted by  Patti     Has the vet said he is healthy? If so I would just make sure he has plenty to eat.   |  
 
  ^^^  I agree....give him access to as much as the amount listed on the bag for a puppy of his size, though mine would never have eaten that much!  (Still, let him eat as much as he wants up to what is listed on the bag!) 
I'm also wondering about the reason for using that specific food.....it only has 21% protein and most puppy foods have closer to 28%.  It also only has 10% fat and most puppy foods have more like 17% or so.....and fat is needed for brain growth in babies.  I'd ask my vet about the food you are feeding and what he thinks about his weight/health.   
He is pretty tiny and probably always will be, so you'll have to be more concerned about his health than with a larger dog.  Because he is so small and so young, you should probably be feeding him at the very least 3 meals a day and maybe more like 4 so that he doesn't get hypoglycemic...smaller pups tend to have a bigger problem with that, so make sure you have nutrical or honey on hand just in case!