Hi you are probably suffering from naso bronchial allergy. It is a condition which effects a lot of people and results in persistent cough and cold, more so with the change of the season.Basically it is the result of overproduction of allergy antibody i.e Ig E in the body. Lot of research is going on in for the role of vitamin C and vitamin E to raise the immunity of the person,although nothing conclusive has come up. You can try Vitamin E for few weeks, it may help a bit, but remember it is not a water soluble vitamin so can accumulate in the body if taken for long periods to cause side effects. Please get the basic investigations done to see if there is a modifiable cause to your problem. Hope it helps.