40 years ago I had a Bencard allergy test (20 pinpricks with various allergens) which highlighted several flowers and tree pollen as my main trigger. Silver Birch pollen is particularly bad for most sufferers. Willow pollen and Aspirin makes me wheezy as well which is a nuisance as many foreign camp sites use Willows to shade the pitches and Willows are a source of Aspirin. I take Tesco One-a-Day Loratadine which helps.
The dry hot weather has made my 'season' early this year due to early flowering.
Evenings are bad as much pollen rises all day in the hot air and then drops back as the air cools. One reason that I detest evening BBQs.