For information on how to track down the causes of and how to eliminate the sources of nasal allergies, excessive sneezing, and chronic allergic coughs, see the allergy section here on AskDrSears.com . For information on other aspects of allergies, food allergies, and understanding what situations are likely NOT allergies, see here.
For a complete guide to understanding and solving every aspect of allergic disorders, check out The Allergy Book here (Dr. Bob sends you a signed copy himself).