Why does my dog have diarrhea?

my dog is 6 months old. and he was perfectly fine yesterday like his usual self. And he even got a recent checkup and they said he was perfectly healthy. Then today he hasnt been full of energy like he usually is and he seems slow. And he has been having diarrhea and its like red and yellow. And i dont know why. Yesterday my mom was trying to cut his hair but he kept moving so she fed him some nacho cheese doritos so he could be distract him. But it was only like 1 or 2 dorito chips. So i dont know if its because of that. So can you guys tell me what could be the cause of his diarrhea?