I used to get bad colds and after getting a really bad one about 15 years ago, I decided to try to do something about it. I did some researched and came up with a combination that has kept me cold free ever since. I don't buy cold medicine anymore! I eat more garlic than the average person, I like it too. I eat more hot peppers then the average person, which I also like. What I had to get used to was drinking 2 cups of water in a glass with a shot (about a tablespoon) of apple cider vinegar in it. My breakfast consists of about 1 - 1.5 cups of milk in cereal, a cup of coffee and the vinegar water. This gets me hydrated well for the day too. So, either the combination of those or maybe just a couple of those have kept me cold free for 15 years now. I teach college courses for a living and am exposed to alot of sick people too.
Also I have asthma. I used to take singulair and other daily medicine for it. I found that I was averaging 4 - 5 bronchial infections a year. I stopped taking the daily medicines and make sure I have the asthma attack medicine available. I try to avoid my asthma triggers. My infections would start after a asthma episode. I'm down to about 1 infections a year when I get it irritated from something like someone burning trash and I drive though it in the car.
I hope this is helpful.