I have been in this same situation a few times--I nearly had the air in our home tested because I wondered if there was something in the air making them sick! Sounds crazy, but I was desperate. Now that your son's been on antibiotics, get him a good probiotic, which will build up his immune system naturally (because the antibiotics destroy both good AND bad bacteria, and your immune system depends upon the good ones!) After illness and meds this winter, I gave my kids a brand called Culterelle. Got it at the local health food store, but you can probably get it cheaper online, maybe at iherb.com? I like it because it's a powder form, so you just stir it into their drink--gave my kids juice and they couldn't taste the difference. Good luck to you. P.S. I have a friend in Australia who recently told me about something called Manuka honey---she said the good stuff can be expensive, but that it's great for colds, flu, etc. I am going to buy some for this winter, in preparation. Ugh.