A. I could be several things. The most common is a gastrointestinal infection which could be treated quiet easily with meds and special food.
Second option could be a foreign body in the stomach or intestine, this object will need surgery to be removed (sometimes possible with endoscopy as well).
Another possibility would be pancreatitis which can also cause liver damage. This is usually a painful condition as well.
Last in the list (although other reasons are still possible) is a tumor in the GI tract. This disease is the worst in the list and has very poor prognosis.
Bottom line each and everyone of those conditions needs a vet visit in order to be diagnosed and treated.
Your account has been reactivated.