He does have a pretty good fever. Normal is 100-102. > 103 is considered a fever. My guess is that it's a stomach bug or intestinal bug causing the nausea, reluctance to open his mouth and fever.
The one thing to be aware of is Parvo
VIrus. This is a common virus in young dogs/ puppies that are not vaccinated. Usually we see vomiting, diarrhea, lethargy and anorexia with Parvo. If signs persist, then he should be seen and treated right away.
If you want to give something tonight for the nausea, you can give over the counter Pepcid ac (Famotidine
) at 0.25 mg per lb every 12-24 hours.
If no improvement by morning, then I would get him seen and started on antibiotics and other meds (GI protectants, pain meds) as needed.
I hope this helps, let me know if you have any other questions.