My Two Year Old Just Had Surgery And They Gave

My two year old just had surgery and they gave him several medications. Now he's experiencing watery, foamy/frothy diarrhea. We thought it was the antibiotics since they always mess with his stomach the few times he's had to take them. He's been of of them for three days and the symptoms are still there. I tried getting a hold of his ped, but I never heard back.