It sounds like Gastroenteritis, Please start with Tab.Rantac 150 mg half tab twice a day for 3 days; Tab.Perinorm 10 mg 1 tab twice a day until vomiting stops and Cap.Sporidex 500 mg 1 capsule twice a day for 3 days,
Next Steps
If the condition doesn't improve please consult ur vet
Health Tips
After medication don't feed him for 2 hours.