Has he over eaten? Is he drinking alot? can he sleep ok or is he moving around and not able to sleep.
Sadie got into my older dogs food and ate WAY to much as a young puppy...(She was 11 weeks at the time)
I had to take her to the er vet. They thought her stomach might rupture!
It was horrible and scary but she was ok. If your puppy has a HUGE tummy and you KNOW something is wrong you should try to get to an er vet.
On the other had, Sadie has a fairly round belly all the time. Maybe what you are talking about is just puppy chubby belly?
I knew something was wrong with her... There was no mistake.