Friend, vomiting can be caused by many different conditions. It can be caused by primary problems in the gastrointestinal tract or secondary to systemic diseases. Common causes are: A simple gastritis, dietary indiscretion, pancreatitis, ingestion of a foreign body, infections, kidney or liver disease, etc. to name a few causes. The fact that this has been ongoing for 3 days I am concern about his hydration.
I would recommend having him re-checked today by family vet for some testing (xrays and blood work) as initial screening test. Pending test results the vet will start him on supportive care (IV fluids, anti emetics, etc.). In the meantime, in any case of vomiting the first thing to do is give the stomach time to rest. This is what you can do:
1- Do not give things like Pepto Bismol. Start him on Pepcid AC (famotidine) 10mg 1/4 tablet every 12 hours. You can buy Pepcid AC over the counter in any pharmacy.
2- No food or water for 3-4 hours. Need to give his gastrointestinal tract time to rest.
3- After 3-4 hours offer a small amount of water. Wait half hour, if no vomiting, offer small amount of rice (50%) and boiled boneless chicken or ground beef (50%) 4-6 times a day. Keep on this diet for several days then wean into regular diet.
4- Follow up with your family veterinarian for a hands on examination.
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