Wow! I so understand where you are coming from. It is just exhausting and we have been there. Here are some of the things I have found work for us.
Echinacea - this helps if you take it the very first second you think you are coming down with something
Zinc - I am not sure if this does much but I always take for the duration of an illness
Vitamin C - Does help boost immunity
Elderberry Extract - I swear every time my kids get something and I give them this the duration is shorter.
As far as eating healthy, you are totally on the right track. Try going one step further and do all organic, zero canned or frozen veggies or fruit. Avoid boxed foods, eat organic oatmeal once a day, drink purified and flouride-free water (8 glasses per day), juice twice per day (grind and press juicer or puree, centrifugal does not benefit as much) and get enough rest!
Some other thought are to take down your dairy and meat intake and cut out salt and refined sugar.
I actually took out any multi-vitamins and supplements as well but will on occasion do an all-natural, vegan shake.
This is sort of a brief breakdown but it may help, it did with us.
Good luck!