L.B.
I recommend Vit A, C, E Zinc and selenium. You can find a good immune formula at fruitful yield, just look for those to be in it. When feeling colds coming on, it is okay to take up to a full gram of Vit C as an adult and 1/2 that for child. Echinacea is also very good. Regular chiropractic adjustments also help tremendously with keeping the immune system working at its best. The reason is because the adjustments clear out any interference in the nervous system which actually boosts the functioning of the immune system and decreases your susceptibility to all the pescky colds, sinus and ear infections out there. I am a chiropractor in Villa Park. If you would like more info let me know. If you need help finding a chiro closer to you again let me know and I will help.
Dr B.