Here's my best advice coming after years of working around kids. I've been taking Oil of Oregano and Colloidal Silver for about 10 years now, and I swear by their effectiveness in preventing/alleviating colds and sinus infections.
But do the research yourself. I'll just point you to one good article that comes up after you google "'Oil of Oragano'" to kill colds"
or "'Colloidal Silver' to kill colds'"
Too good to be true?
You really should decide that for yourself. But like I said, I swear by both. And for friends that I've recommended these alternative therapies to, they've thanked me after having tried them.