My Father In Law Has Been Having Severe Diarrhea For

My father in law has been having severe diarrhea for 2 weeks, and a flare up of cellulitis on his legs, but refuses to go to the doctor He has a history of DM type 2 which he takes Metformin. He reports no new medications or different eating habits to explain diarrhea. What should we look for or what might be causing his symptoms?