Diarrhea with no other symptoms…

Almost 6 year old, male, neutered started having diarrhea last weekend. Was barely eating the first day, but by day 2 was back to eating, drinking, playing, etc. He doesn’t appear to be straining in the litter box. Taken to the vet, no elevated temperature. Prescribed antibiotics and probiotic, but hasn’t improved after 3 days. Any thoughts on what we can do to help? Calling vet again tomorrow about scheduling bloodwork.