Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your fellow is vomiting, has a poor appetite for his own food, and drinking more water than usual.
A sore tooth should not cause him to vomit, and most dogs with a tooth problem simply eat around the sore tooth. Unless his whole mouth (gums and teeth) are horribly infected I would not expect that to change his appetite.
Some antibiotics could cause a decrease in appetite, and vomiting can lead to dehydration, so he would want to drink more, but since he has now been off the antibiotic for a week he should be better, and that doesn't seem to be the case.
Lack of an appetite and vomiting and increased water consumption can be related to eating something he should not have, too many treats or table food, eating foreign material (which could cause a full or partial gastrointestinal obstruction), chronic pancreatitis, toxin exposure, a viral or bacterial infection, organ failure, diabetes, Addison's disease (hypoadrenocorticism), inflammatory bowel disease, or even infiltrative cancers such as lymphoma.
Because he hasn't eaten normally in several days and he is drinking more I am very concerned about him.
Ideally he would see his veterinarian today for a recheck since this has been going on for more than 72 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.
In the meantime they can administer injectable anti-nausea drugs.
If you cannot have him seen for whatever reason right away there are some things you can try at home.
At home to try and settle his stomach you can give either:
1) Pepcid ac (famotidine) at a dose of one 10mg tablet per 20 to 40 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 are acid reducers and may help him feel less nauseous so that he will eat and not vomit. They are quite safe and can be used for several days if necessary.
A couple of hours after giving the acid reducer I recommend offering meat baby foods or a bland diet of 1/3 boiled, minced, white skinless chicken or boiled, lean hamburger and 2/3 boiled white rice mixed with some low salt chicken or beef broth to make it easy to lap up and swallow.
If he continues to not eat normally he should see her veterinarian for an examination, diagnostics and intravenous fluids and supportive care.
Please let me know if you have any further questions.