Hello, my name is***** and I have over 20 years of experience as a veterinarian.
I am very sorry to hear about your pup Gunner's whining and stretching. By stretching I assume you mean that he is extending his front legs with his chest down towards the ground and his rear end up in the air.
The front legs and chest down, rear end up in the air position is called a prayer bow and is often an indication of abdominal pain. This seems likely along with his whining and inability to settle. It is a stretching motion attempting to relieve pressure/pain in the abdomen.
In cases like this where the dog acts uncomfortable it is likely that the pup is experiencing some reflux or abnormal motility, or painful intestinal spasms that are more than the usual. In severe cases this can be linked to pancreatitis which is a painful inflammation of the pancreas leading to increased enzyme leakage.
Possible causes of nausea and abdominal pain include a change in diet, dietary sensitivities or allergies, or eating things that they should not like too many fatty table scraps or garbage, bones etc. Addison's which is a poorly functioning adrenal gland is another possibility for waxing and waning abdominal pain, vomiting and nausea. Metabolic organ failures (kidney or liver disease), pancreatitis, inflammatory bowel disease or even infiltrative cancers are possible causes as well.
Has he eaten anything he should not have recently (toy pieces, bones, garbage)?
Any changes in food or treats?
You can give him an acid reducer to try and settle his stomach. Either:
1) Pepcid-ac (famotidine) at a dose of one half of a 10mg tablet per 10 to 20 pounds of body weight every 12 hours.
2) Prilosec (omeprazole) at a dose of one half of a 20mg tablet per 20 to 40 pounds of body weight every 24 hours.
Either of these will reduce stomach acid and could help settle his stomach. These can be used long term if necessary as they are very safe.
I'd also pick up his food and water for now. A couple hours after one of the acid reducers you can offer small amounts of water or ice cubes to lick.
No food for 12 hours. Small amounts of water only.
After his food fast if he seems to feel better then start a bland diet of 1/3 boiled, lean hamburger (or boiled, white, skinless chicken) and 2/3 boiled white rice. Give small meals several times a day. Feed the bland diet for several days, then start mixing in his regular diet and slowly convert him back.
If his nausea and abdominal pain continues then he may need injectable medication from his veterinarian to get his stomach upset under control.
So watch him for continued symptoms even with the acid reducers, blood in his stool or vomit or a fever (more than 103.5F rectally), a tense painful belly, a rapidly swelling, tight abdomen with attempts to vomit that are unproductive, or lack of appetite after his food fast. If any of those occur it is time to seek hands on veterinary care on an emergency basis.
Please let me know if you have any further questions.