Does he use drugs, specifically marijuana?Food allergies? It would be a bit drastic, and may not explain the swelling, but you can develop them at any time.A bit young for cancers, but maybe he is genetically predisposed, getting at least a CT scan with contrast of his abdomen would be good.This is concerning for his heart too, as mentioned.He needs quick workup, as mentioned. Worrisome is not eating and what his electrolytes are like.Not that being obese is the sole cause of his symptoms, but he should lose weight. Almost every physician you will run into will say this as it is important for his health, just as they would tell him to stop smoking if he was smoking.
As the physicians here have responded, go to ERnow. And please update! Very curious to hear his outcomes. Best of luck to you