Side/back pain of a 80 year old increasing symptoms

Patient: My grandfather who is 80 and also an alzheimer’s patient, has recently been complaining of pain located in his left side lower rib section, but directly on the side. Last week starting Sunday he had a severely decreased appetite along with vomiting once. Since then he is barely eating but his thirst has increased. We haven’t noticed a fever but he has of course been increasingly week. He went to the doctors last week but I don’t think they found anything. What could be causing all of this?

Symptoms: Lack of appetite. Increased thirst. Pain strong enough that he can’t get comfortable in his chair. Weakness.