just thinking a bit more (always dangerous) --
I had four years of allergy shots as an adult, and the allergist told me that it's pretty much a crap shoot. My words, not his. That the shots will help me, maybe for a lifetime and maybe for just a while. Because i could develop new allergies or redevelop the old ones. That even as an adult, things are changing.
Where I currently live, people who previously had no environmental allergies and move here can suddenly develop them. I live near a major river.
So far, the shots have helped me for the most part --- but a few of them didn't "take" --- for example, my cat allergy. Highly allergic to cats but if I stay away from them (as in, do NOT pet them) then I am okay ---
(unless I stay overnight with someone who has four cats that roam the house . . . which I did one time and pretty much struggled for breath by morning).
But I do not have the problems I once did with my environmentals, in general.
Mom2, you probably would NOT want your son to be off the antihistamine in the fall for testing, if he tends to have allergy problems in the fall.