Friend, vomiting can be caused by many different 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: A simple gastritis, dietary indiscretion, ingestion of a foreign body, infections, etc. to name a few causes. If he is lethargic to the point where he does not want or is reluctant to walk I would have him checked by ER veterinarian. Attending veterinarian may need to do some testing like blood work and xrays to determine the exact underlying cause. If you do not have access to ER vet this is what you can do until he is seen by family veterinarian. 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 8-12 hours. Need to give his gastrointestinal tract time to rest.
3- After 8-12 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 family veterinarian for a hands on examination.
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