I'm a certified canine nutritionist, and what you absolutely must address first is
why your dog is vomiting and isn't eating properly.
Please don't be offended by this.
Supplements won't address the root cause, and even if they improve your dog's symptoms all you would be doing is masking the symptoms.
It sounds like you've visited your vet which is a good first step, but also sounds like you've been given bad advice. I would recommend considering the following assuming your vet didn't find any other health concerns:
- What food are you feeding your dog? You'd be surprised how many people don't consider diet as the cause of symptoms such as this, but it's very often the cause.
- Are there any environmental factors which could cause these symptoms? i.e. do you clean your floors with chemicals and then let your dog lick food off the floor - this may sound obvious, but happens more that you'd think.
Have a good long think about your dog, their diet over the years, age, and so forth. It's best to think of your dog as a carnivorous meat-eating animal, yet it's likely your dog food is made of cheaper ingredients such as poor quality meats but most likely far more grains and other ingredients which are hard for your dog to digest. When you think of it that way, it comes as no surprise how vomiting and gastrointestinal discomfort is so common.
Even when changing to a better diet - more expensive kibble, raw, homemade or so forth - it can still take a very long time for a dog's gut to heal.