What Causes Chronic Diarrhea After Taking Nu Lax Laxative?

Before my dad was constipated. But after he took Nulax fruit laxative he often has diarrhea every four days. He already stopped taking Nulax but still the diarrhea is occuring every four days, i would like to ask can eggs or egg white causes diarrhea? I often cook something and i put century egg in it will it causes him to have diarrhea, just recently he was diagnosed having stone in d gallblader will be this causing diarrhea? Pls reply, thank you doctor. I am angie the daughter of the patient.