J.C.
I just had this stomach flu a couple of weeks ago and it took me a full 6 days to regain my appetite; I imagine it would take longer for your boy to get over it (probably up to 2 weeks). I know it is a pain, but I would recommend pumping to maintain your supply until he gets his appetite back. I know when I was starting to feel better I only wanted certain bland foods, and no dairy to speak of.