Has anything happened recently to mess with his gut flora -- a course of antibiotics, or other meds?
I second the probiotics recommendation.
If I never feel another foldable crate banging against my shins as my dog pulls on his leash and my carrier bag slips off my shoulder, it will be too soon, that's all I can say.
Also let’s not forget the shleping. Sometimes in the rain or 100 degree weather.