Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you with your wee one today.
I share your concern about Knuckles.
Now it is good that he has stopped vomiting, but if he is reluctant to eat, then nausea (even without vomiting) would be suspect and may need to be addressed. To do so, you can consider a trial on an antacid. There are a number of antacids that are available over the counter and pet friendly. I would advise only treating with one, but the two I tend to recommend are Pepcid (More Info/Dose) or Zantac (More Info/Dose). This medication of course shouldn’t be given without consulting your vet if he does have any pre-existing conditions or is on any other medications besides the antibiotics. Ideally, it should be given about 30 minutes before food to ease his upset stomach.
Once that is on board, you can try to tempt him with a light/easily digestible diet. Examples of this would be cooked white rice with boiled chicken, boiled white fish, scrambled eggs (made with water and not milk), meat baby food (do avoid the ones with garlic powder in the ingredients) or there are also veterinary prescription diets that can be used in cases of gastroenteritis, notable Hill’s I/D or Royal Canin’s sensitivity. When offering food, just offer small meals at a time and let him have breaks (~30 minutes) to ensure he keeps down what food he will eat for you.
Hopefully, he will be tempted to eat once his stomach settles. Though if he still refuses and isn't vomiting then we may have to consider initiating syringe feeds to get food in. In that case, you may want to try Hill's A/D (LINK) from your local vet. This is a critical care diet that is comes as a soft, palatable pate. It is calorically dense, so a little goes a long way nutrition-wise and this could just help get some more calories into her even if we can’t get a huge volume of food in. As well, for syringing food, you can use the animal version of Ensure (balanced for animals dietary requirements) called Clinicare Canine/Feline Liquid Diet (LINK). It is actually by the same people who make Ensure, but is formulated to meet out pet's dietary needs. Your vet should be able to order it for you but it is available without a prescription. Alternatively, as a short term means, you can also offer wet puppy food or meat baby food. If he wont' eat them directly, they can be watered down and syringe fed to him. This way it would a means of getting food/fluids in, staving off dehydration/weight loss, and buying you time to uncover the reason for his loss of appetite.
As well, do keep an eye on his water intake. You did mention that he is drinking, but we do want to make sure he is drinking enough to avoid dehydration. Therefore, at this point you do want to check his hydration status. To do so, there are a few things we can test for at home. One is whether the eyes appear sunken, if the gums are tacky instead of wet/moist, and whether he has a "skin tent" when you lift the skin. To see how to check these parameters for dehydration, you can find a wee video on this HERE. If he is showing those dehydration signs at this point, that is our cue to have him to the vet before this can get any worse. If his hydration looks normal, then we'd want to keep encouraging him to drink with fresh water +/- low salt chicken broth.
Overall, I share your concern that this underlying nausea has been lurking for too long already. Therefore, as we do want to see if we can get him back on his food as soon as possible, I would advise the above. If you initiate these treatments and do not see improvement over the next 12-24 hours, the it would be best to speak to his vet again. Antibiotics could help if this was bacterial, but if he isn't settling then we have to consider other issues (ie viruses, pancreatitis, foreign bodies, metabolic disease, organ issues, toxins, etc) and in that case, we'd want them to reassess him and consider at least treating him with an anti-vomiting injection +/- appetite stimulants to settle this for him.
I hope this information is helpful.
If you need any additional information, do not hesitate to ask!
All the best,
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