Hello, my name is***** and I have over 20 years of experience as a veterinarian.
I am very sorry to hear about your pup Chief's episodes of vomiting, lack of appetite, and extending his front legs out with his chest down with 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 in a dog when he is showing the other things that you are seeing. It is a stretching motion attempting to relieve pressure/pain in the abdomen.
Possible causes of nausea and abdominal pain include a change in diet, dietary sensitivities or allergies, viral or bacterial infections, or eating things that they should not like too many fatty table scraps or garbage, bones, foreign material etc. Addison's which is a poorly functioning adrenal gland is another possibility for waxing and waning vomiting and nausea. Metabolic organ failures (kidney or liver disease), pancreatitis, inflammatory bowel disease or even infiltrative cancers are possible causes as well but very unlikely at his young age.
I know he has a history of shredding things but has he eaten anything he should not have recently (toy pieces, bones, garbage)?
Any changes in food or treats?
Ideally he would see a veterinarian today since this has been going on for more than 48 hours. Simple stomach upset should pass within 24 to 48 hours. They could examine him, run blood tests and possibly check radiographs and/or an ultrasound to evaluate him and know best how to treat him.
If you cannot have him examined today there are some things that you can try, but with history I am worried about a gastrointestinal obstruction and those should be dealt with promptly.
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.
These will reduce stomach acid and may help settle his stomach. These can be used for several days if necessary as they are very safe.
I'd also pick up her food and water for now. A couple hours after one of the acid reducers you can offer small amounts of water, clear broth, or ice cubes to lick.
No food for a few hours. Small amounts of water only.
After his food fast then start a bland diet of 1/3 boiled, lean hamburger (or boiled, white, skinless chicken) and 2/3 boiled white rice or well cooked plain pasta. 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 needs to see a veterinarian for hands on care, including an examination, possible radiographs, and injectable medication from his veterinarian to get her stomach upset under control as well as fluids.
So watch him closely 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 or a continued lack of appetite after his food fast. If any of those occur it is time to seek hands on veterinary care.
Please let me know if you have any further questions.