The culprit behind your allergies probably isn't outside. It's in your bedroom! According to the Asthma and Allergy Foundation of America, about 20 million Americans are allergic to dust mites.
What can you do? Wash your bedding once a week in hot water to kill dust mites. This will also clean off any pollen or other allergens that may be on them. In order to really solve the problem, you can also switch to hypoallergenic bedding. Here is a quick guide to choosing hypoallergenic bedding.