It sounds like you are doing all the right things.
I agree with the other posts about BRAT diet, etc., but I have one more recommendation that you might want to ask your Dr. about.
Typically with viruses, dairy is bad. BUT, that Yobaby yogurt is loaded with live cultures that can really help straighten out a stomach. If you could build up the good bacterias in his stomach with yogurt or some of that baby-dophilus (sp) pro-biotics, that might help regain control over his intestines and overpower whatever bugs he has growing in there. I would just ask the Dr. first before doing the yogurt.
We had a diarrhea problem a couple of weeks ago and after the 300th outfit, I decided to go for it with the yogurt and saw a same day improvement. BUT our diarrhea was anti-biotic related, not viral.
Good luck, I hope he gets to feeling better soon!