Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am very sorry to hear about Sammy's upset stomach and "hang dog" look.
Common causes of nausea are a quick change in diet, too many treats, especially fatty or spicy treats, eatings things they should not such as things found in the yard, toy pieces or garbage, viral or bacterial or parasitic infections.
More serious causes include chronic pancreatitis, a dietary allergy or sensitivity, inflammatory bowel disease, internal organ failure (kidney or liver disease), a full or partial gastrointestinal obstruction or even infiltrative cancers such as lymphoma.
At this point we can try some things at home but he may need to see a veterinarian if he isn't coming along well.
To try and settle his stomach now you can give either:
1) Pepcid-ac (famotidine) at a dose of one 10mg tablet per 20 to 40 pounds of body weight every 12 hours. I would give four of the 10mg tablets every 12 hours to a pup his size.
2) Prilosec (omeprazole) at a dose of one 20mg tablet per 40 to 80 pounds of body weight every 24 hours. I would give two of the 20mg tablets to a pup his size once daily.
These will reduce stomach acid and should help if this is related to simple nausea and gastrointestinal irritation from eating something he should not have.
I would not feed him any food for 12 hours even after the acid reducers are started.
This should help stop gut spasms and restore normal gut motility.
Starting a couple hours after the acid reducers small amounts of water or ice cubes given frequently are fine as he needs fluids.
You can give pedialyte to replace electrolytes too.
If things are going well after his food fast and the acid reducers start a bland diet of 1/3 boiled hamburger (or white skinless chicken), all fats and juices drained off mixed with 2/3 boiled, plain white rice. Feed several small meals a day. Once he feels better (no vomiting for 48 to 72 hours) start mixing in his regular dog food very slowly. Less bland more regular with each day. It should take a week or so to convert him back.
If Sammy starts vomiting and is feeling poorly though, it would be best that he see a veterinarian now as anything you give him orally will just come back up leading to dehydration.
If he has a tense painful abdomen, becomes very lethargic, begins vomiting, or runs a fever greater than 103.5F then he really must be seen by a veterinarian as soon as possible.
Best of luck with your fellow, please let me know should you have any further questions.