Antibiotics are sort of a "catch all".. if a vet doesn't really know what's going on, basically the first thing they'll do is throw some antibiotics at it.
I'd probably try some Slippery Elm to sooth his GI tract, and a really high quality probiotic like Primal Defence Ultra.
I'd probably try some Slippery Elm to sooth his GI tract, and a really high quality probiotic like Primal Defence Ultra.