Allergies. Pollen counts are rising in my neck of the woods too -- zyrtec is a good start, but i would also consider an age-appropriate nasal steroid -- see your family doctor or pediatrician for advice -- help is out there!
Itchy kid. Take him to a pediatric allergist to help identify the culprit. It may be something other than pollen. He is not too young for immunotherapy. Some doctors provide sublingual immunotherapy though this is not approved generally in the us.