It's rare for me to get a sinus infection, and that only happens when I get a bad case of the flu (Influenza).
I'm curious do you have allergies and such normally? Perhaps your immune system overreacts to something related to the hobby due to a predisposed response. I know my sister's immune system overreacts on many things, and she claims air purifiers help some (of course medication does more so). Might be worth checking into.
Do you breed feeder roaches? I can't imagine anyone being allergic to mantids but the dust created by a large colony of roaches, especially if they're kept dry, is some pretty nasty stuff.