You've found a really good place to come and learn. Congrats on your new puppy . . .
While it is an exciting time for you and your family, the puppy is probably just nervous and scared not knowing of his new surroundings, it'll take time for him to adjust and get used to your daily life and his new home. Since you purchased him from a pet store, he's probably not been used to people and noises and such. The first thing you should do in the morning is set up a wellness visit with a vet you will be using so he can be examined to make sure he is healthy and to get his statistics. It would also be wise to bring a poo sample so it can be tested for any parasites. If you don't feel he's eating well enough, you can always supplement his food with some broiled plain chicken or turkey that really gets them going!
Congrats again and keep us posted of his progress. What's his name?