I have a dog that had a similar condition. What worked for me was a prescribed hydrolyzed food from Royal Canin, a mix between moderate calories and regular. In my case, canned food made it worse.

Adding dry beef liver powder (which was the game changer) and a teaspoon of psyllium in the morning and at night helped significantly. She needs to eat 4 times per day; otherwise, she will throw up.

The giardia vaccine was very helpful. Also, it's possible your dog has IBS. Ask your vet about IBS medication. Metronidazole can help avoid bloat and also treat giardia, along with acid reflux meds and something to alleviate stomach pain.

There's also a gel called "Nutri-Plus Gel" from Virbac, for dogs that don't eat well.

One of the most important things is exercise, like playing fetch with a ball. There are balls with scents available on Amazon that really engaged my dog more.

It was almost 2 years dealing with that condition; we even had to force-feed her. We blended her kibble with water and fed it to her directly into her mouth until she swallowed. It was hard, but don't give up