This is gonna sound weird...
Garlic. Raw garlic - cut it up in pill sized chunks and take it like pills (careful to make it small-ish pill-sized chunks). It's an antibacterial and an antiviral. When I start to feel something coming on, I have a clove or two in the morning and again at night. Also, you can do "garlic tea" which is basically a crushed clove of garlic that you pour hot water over (I do it in my tea pot) and let it steep for a half hour or so? Then, add honey and lemon to taste. Not overly delicious, but it does the trick, usually, for me.
Also, for congestion relief? I use RC oil on my feet... it's the "respiratory congestion" essential oil mix from young living. I mix it with coconut oil and slather it on, then put on socks.
Have you heard of wet sock therapy? It's supposed to be awesome, but I've never tried it.
http://www.heartlandnaturopathic.com/coldsock.htm
Then there's the neti pot... a little baking soda (like a tiny, tiny pinch) in a neti pot helps the congestion clear out faster. Or in lieu of a neti pot, you can pour yourself a cup of warm-ish water add some sea salt and the baking soda and snort it instead. Not overly comfortable, but it can do the trick...
