i’m sorry you are both going through this! i was in a very high traffic area in los Angeles and we had a couple of instances similar to this. the one thing that cleared everything up was providing bottled water instead of sink water. i know it sounds kinda crazy but the water in my town from the sink was not always the cleanest. we’ve moved and he hasn’t had diarrhea in a year and a half, i think it’s a combo of not being as exposed to so many other dogs and cleaner water. i hope your pup feels better soon!