If there is any distended or bloated stomach, I strongly recommend you go to an ER vet right now. Absolutely, no wait and see. A bloated or swollen stomach can be due to stomach bloat, stomach torsion, fluid build up in the belly (ascites), organ enlargement or a tumor.
It's okay that he hasn't eaten anything considering the recent vomiting.
To help settle the stomach you can use of the following, but not as a replacement for veterinary examination include
1.Pepcid A.C. (famotidine) comes in 10mg, 20mg, or 40mg tablets.
You can give it every 12 hours. You can give 0.5mg per pound of body weight. So, a 20 pound dog would get 10mg.
2.Prilosec (omeprazole). It comes in 10mg or 20mg tablets.
You can give in every 24 hours. You give 0.5mg per pound of body weight. So, a 20 pound dog would get 10mg
3.Zantac (Ranitidne). It comes in 75mg, 150mg, or 300mg sizes.
You can give it every 8 to 12 hours. You give 0.25 to 1mg per pound of body weight. So, a 20 pound dog would get roughly 1/3 tablet of the 75mg. Even with bigger pets, it is easiest to get the smallest size tablet. Even a 75 pound dog would only need one 75mg tablet.
4.Pepto-Bismol or Kaopectate
You can give it every 8 hours. The average dose is 1ml per pound of body weight, and that is the TOTAL dose for the day.So, if a pet weighs 30 pounds, they would get a total of 30ml a day or 10ml every 8 hours. This is dosing for regular strength Pepto-Bismol. If you use maximum strength liquid, give half as much.
Definitely, worth the ER trip even if you try to give one of the above antacids.
If the vet agrees about the belly, they will very likely encourage some abdominal x-rays which will get you some answers quite quickly.