Hello, my name is***** and I have over 20 years of experience as a veterinarian. I'm sorry to hear that your girl isn't feeling well and is lethargic, refusing to eat and vomiting.Vomiting can be related to eating something she should not have, too many treats or table food
, eating foreign material (which could cause a full or partial gastrointestinal obstruction), chronic pancreatitis, esophageal reflux, a dietary allergy or sensitivity, toxin exposure, a viral or bacterial infection, inflammatory bowel disease, heartworm
(a tumor of the thyroid gland) internal organ failure, or even infiltrative cancers such as lymphoma.Since she isn't able to keep even water down she will quickly become dehydrated, especially because she is vomiting as well, and as her liver breaks down fats to live she may develop a type of liver disease called hepatic lipidosis. This can be fatal if not treated aggressively.Ideally she would see a veterinarian since this has persisted more than 24 hours if the Cerenia isn't working. Cerenia is a potent anti-nausea medication. Simple stomach upset should pass within 24 to 48 hours. They could examine her, run blood tests and possibly check radiographs and/or an ultrasound to evaluate her and know best how to treat her.In the meantime they can administer injectable anti-nausea drugs and fluids to rehydrate him.If that absolutely isn't possible today there are some things you can try at home.At home to try and settle her stomach you can give either:1) Pepcid ac (famotidine) at a dose of ¼ of a 10mg tablet per 5 to 10 pounds of body weight every 12 hoursOR2) Prilosec (omeprazole) at a dose of ¼ of a 10mg tablet per 5 to 10 pounds of body weight every 24 hoursThese are acid reducers and may help her feel less nauseous so that she will eat and hopefully not vomit. They are quite safe and can be used for several days if necessary.You can use a medicine syringe to try and force water into her orally a couple hours after giving her one of the acid reducers.12 hours after giving the acid reducer I recommend offering meat baby foods or a bland diet of 2/3 boiled, minced, white skinless chicken and 1/3 boiled white rice mixed with some low salt chicken broth to make it easy to lap up and swallow.If she continues to not eat or continues vomiting she should see a veterinarian for an examination, diagnostics and intravenous fluids and supportive care.Please let me know if you have any further questions.