M.B.
Yep - please stop the milk - it can be very tough on the gut and can be a huge contributor to increased GI problems, even without a flu. Also, remember the BRAT diet for these sorts of things: Bananas, rice, apples, and toast. You might try giving him some cinnamon raisin toast - my kids love it. Also, cream of rice cereal might work. The pedialyte is a good idea. Also, homemade chicken soup is great, although even canned campbell's chicken noodle is good.
Also, there are some good natural nasal sprays. This is my favorite:
And, finally, when my kids show any signs of these bugs, I give them Sambucol - it's an elderberry extract developed in Israel that research shows is a potent anti-viral.
Also, as long as you can keep fluids in him, it's not the worst thing in the world for him to not be eating much - he's instinctively letting his GI system rest. And, finally, please consider giving him probiotics to replenish the healthy gut bacteria. Remember 70+% of our immune function is our guts.