There is some baby cereal that comes with probiotics. I use Plexus ProBio5 which is a pill that can be pulled apart and added to a bottle or juice drink. For an infant, he would get a quarter of a pill a day.
I have been told that sometimes having diarrhea means that their digestive system is changing. My baby girl just went through it a weeks ago lol. It doesn't hurt to try anything. It could be what @mamawallace1201 said. Just try different things little at a time to see if they do anything and see if they work