hi hun, hope he gets better soon, try to give him water & avoid solids for some time. Plain yoghurt is good to settle his tummy. But if he's not interested dont force him to eat. He will need lots of fluids, cow milk might make it worse. If you want to offer him milk, delute it with some water. It usually takes 24 hrs to settle xx
ETA: Using lactose free milk or formula for 3 days also helps as it's easier to digest than regular milk