What to do?

I've posted a few times in the past month about how Jackson has been sick. Well, unfortunately, it doesn't seem to be letting up. He'll act like he's getting better for a couple days, then his cough comes back with a vengeance and he's started throwing up and has had a fever. I've been to see three doctors, but they've all pretty much told me the same thing: we'll give you this prescription (inhaler, antibiotics) but we can't find anything wrong.

Gah!

It's so frustrating! I don't blame the doctors because if they can't find anything, they can't find anything, but I just want my little man to feel better. It's so sad to see him struggling :o(  I've been trying to stay home and take it easy with him, but I feel like he gets really bored. I don't want to take him anywhere that he can get other kids sick, either. I just don't know what to do for him! Anyone have any great advice?