my puppy was skinny yesterday and today he was rlly fat and?

when he was running arond he was breathing like he was rlly tired.hes a 2 month old sheltie and no i wont take him to the vet if u just post that cause he looked happy with no problems he was normal only he was like kinda fat i dono why is it normal? cause this isnt a vet situation. got him a full jeck 2 days ago and he was healthy so is this normal in puppies cause i never had 1 before

This isn't a vet question? It's a total stranger type of question?

Without knowing specifics, it's difficult to say what happened to your puppy. Did it drink a lot of water? Water can cause bloating. Did it get into the dog food and eat too much?