He might actually sleep quite well, these bugs sometimes wear them out and they don't always feel that hungry.
Once he is hungry and can keep something down you could offer him plain biscuits just to keep him going. I used to stop all dairy but give biscuits or plain, bland meals e.g. chicken and rice (I used baby rice when ds was little) or pasta.
I presume you were told to starve him by a doctor. Any particular reason? I was told not to by NHS Direct. I found ds1 tended to starve himself actually, until he felt like eating again which was usually when the worst was over.
Hope he's better soon.