23 weeks? I'd suspect normal teething as long as there are no other symptoms such as lethargy, vomiting, diarrhea or fevers.
If his lips, gums and tongue start getting pale and dry it is an emergency vet trip not a tomorrow morning get an appointment trip. Puppies also swallow all sorts of things including lost teeth so if he vomits or can not pass stool or has diarrhea, those add up to a possible blockage.He still hasn’t eaten today and he didn’t even finish his breakfast yesterday. I’m taking him to the vet in the morning and they are going to check him out. They told me to give him pepto and to keep an eye on him. He isnt hiding anywhere, just laying around and he looks like he feels bad. It was a sudden change in mood for him, like he was fine yesterday morning and by the time I got off work he wasn’t eating and was acting like he felt bad. I know he lost a tooth earlier today because I found one. His tongue is pale today also