Astragalus is probably a good herb for you to take as a tonic to build up immunity.
Also, if you have seasonal allergies, don't just ignore them. Take quercetin with bromelain as a preventative. You may not even have to take it year round, but just as allergies flair up. Quercetin is a bioflavinoid that occurs naturally in citrus and most foods that contain high amounts of vitamin C. Bromelain is a digestive enzyme (from pineapple) that, taken on an empty stomach, helps with inflammation, as in swollen sinuses.
Gingko is an excellent bronchiodilator that may help allay bronchitis if you catch it early. It is the #1 prescription in Europe for asthma.
Also stay away from known allergens, like pet dander, mold and excessive dust. Second hand smoke can make allergies worse. A diet high in vitamins A, C & E is helpful to boost and maintain immunity.