3 m/o shih tzu hasnt pooped in 24 hours after antibiotics

My poor baby got some stomach bug from the dog park and had diarrhea for two days. They put him on antibiotics and today was his last day taking them . He hasn’t even tried to poop since he did last which was yesterday at 4 am , 5 am now here. He’s acting normal and happy, no visable discomfort when I press his tummy, and still eating and drinking. Vet calling to check in tomorrow but I can’t sleep and hope someone will see this before then. Thanks in advance!!!!