E.W.
My niece had leg pain after being sick, when she was that age, that got so bad she couldn't walk. After air lifting her to a children's hospital and running a myriad of tests they concluded she was dehydrated. After an ivy, she was fine. I would push fluids like crazy with him and watch him carefully. Sure the doctor could have done a flu test, but it's not like anything could be done about it if he had the flu, at that point. (People forget Tamiflu has to be taken the 1st 48 hours to reduce the length of symptoms, and according to their website in children it only reduces it by 1.5 days.) It sounds like he's had it for 5-6 days now, and for 3-4 days when you first took him in, so it wouldn't have done any good. Best advice is to hydrate, rest, and keep a close eye for dehydration/complications. Hope everyone feels better soon!