Hi there, and welcome to YT ! I can't wait to see pictures of your new baby
It is a good idea to free feed your new baby a higher quality puppy food. A kibble diet is best, and good for their little puppy teeth, and emerging teeth .
What has already been said, take him to a good vet too. His swollen belly could be an indication of worms, which is very common in young puppies. It's simply treated by deworming, + a vaccine schedule is good to get him started on right now. Keep training him on the puppy pads , is perfect , because he is too young to be outside, and exposed to other animals. Congradulations on your new puppy .