If you were taking Claritin, Zyrtec or Allegra within a month of getting tested, the results could have been inaccurate. Also, allergy test serums are not standardized, so it is possible to test negative because the dilution of the test serums used may have been too low for your body to mount a response to it. Also, it is known that sometimes the test serums become so old that the proteins that are in the serums break down and are no longer accurate for allergy testing. You might consider asking for a CAP-RAST blood test, which is not usually affected by antihistamines.
Yes, there are other types of reactions to pollens, etc. Type 4 reactions are the IgG reactions. Then there are Type 2 and Type 3 reactions, too - these are not as well-understood.
One thing to possibly consider is consulting a Naturopathic physician and asking for Alcat testing for inhalants (pollen, dust, animal dander, etc.) and foods. Alcat tests look for all types of reactivity, not just Type 1 (IgE-mediated, or "classic" allergies).
Sometimes foods can be cross-reactive with pollens, so you may not be allergic enough to show a reaction on a test for pollens, but when you eat the food that cross reacts during the pollen season, it is like a double whammy and thus you get symptoms.
Another possible test method to look into is NAET (www.naet.com) - I have no financial affiliation with this website or company. It is an acupuncture based allergy testing and treatment method that has a pretty good success rate (about 80%), even with non-IgE allergies.