Tree allergy would probably not produce hives at this time of year. Maybe in the spring.
Have you tried Zyrtec or Benadryl? Those are strong antihistamines. Benadryl can make you drowsy, so I'd try it first in the evening, or sometime when you don't need to be alert.
Where are the hives? Could they possibly be triggered by something you are eating? Medication you are taking? Soap?
