Vomiting can be caused by many different medical conditions. It will be difficult for me to determine the exact underlying cause without a hands-on examination and some testing. But, common causes are pancreatitis, dietary indiscretion, ingestion of a foreign body, infections, or even part of a systemic disease, etc. to name a few causes. If he has been vomiting since yesterday, I would have him checked by your vet for a hands-on examination and some testing (blood work and x-rays) to determine the exact underlying cause. 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 or Imodium. Start him on Pepcid AC (famotidine) 10mg 1/4 tablet every 12 hours for the next 2-3 days. You can buy Pepcid AC over the counter in any pharmacy.
2- No food or water for 4-6 hours. Need to give his gastrointestinal tract time to rest.
3- After 4-6 hours offer a small amount of water. Wait half hour, if no vomiting, offer a 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. If cost is a concerned look into your local ASPCA or Shelter where they often offer veterinary services at a lower cost.
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