My Husband Has Had Diarrhea Off And On For The

my husband has had diarrhea off and on for the last 5 days. He's only eaten a banana, crackers, probiotic drink. He thought he was better today and tried real food. But soon after eating, he had to run to the bathroom. Since then he's been on the toilet off and on for over 3 hours. He's miserable. He's taking Pepto and it's not working. What would you suggest?