A. This is usually a sign of a severe gastrointestinal infection, it could be a bacteria or virus, most likely due to something spoiled he ate. other option are severe pancreatitis or a foreign body ingestion causing irritation and partial blockage.
You need to take him to the vet to make sure it's indeed just an infection and get him an anti vomiting injection as well as antibiotics.
Your account has been reactivated.