Its normal for puppies to be sluggish when they leave their litter mates and first homes. Whenever I take my puppy anywhere, he'll sit in his carrier and avoid coming out for awhile. Luckily for me, all three of my dogs had no trouble coming home and adapting. They all acted as if they owned the place almost right away.
We bought this stuff to put on the dog food when Maddie came home from the breeder, it helps their stomachs and makes them want to eat. You might check it out on the internet.
Its normal and hopefully your puppy will adjust quickly and it won't be a problem. Try to get him to eat and drink his water. Good luck!