D.C.
My pediatrician recommends probiotics to help kids get over diarrhea. He recommends a dusting of Culturelle in with the cereal once a day (an adult capsule, broken open and sprinkled on food should last about 3 days for a baby). The Culturelle can take a few days to work.
Otherwise, BRAT diet is about all you can do that I know of. Note on the BRAT diet - applesauce is helpful for diarrhea, apple juice can make it worse.
As for other things causing it - it could be teething - I assume you didn't change formula recently, or something like that? A formula or other food change could also cause it.
Also, I don't usually comment on other people's posts, but perhaps 1stTimeMommy misunderstood your post, because all the things that she recommends are things I've heard of to help constipation, and could make the diarrhea worse. Please don't try them.
You don't know either her or I to trust our advice implicitly, which is a reminder that you should run all ideas past your pediatrician before you give your baby any kind of natural (or unnatural) remedy...