I went to see an allergy specialist, who worked out exactly what I was allergic to.
Obviously grass and pollen were high, but there were also a number of other "lower level" allergies that I had, but was unaware of (and that most other people probably have too).
Yeast
Wheat
Sugar
House dust
Fungus spores
...
The list was pretty mad, none of which registered less than 80 on the scale (0 to 100, 0 being completely, probably fatally, allergic to something), pollen scored a pretty abysmal 20, as did fungus spores, etc.
The idea behind the treatment is to cut out all the foods/whatever causing the lower level allergic reactions, which leaves your immune system better equipped to deal with the higher level ones that you CANNOT avoid.
I was off sugar (including all fruit, etc), yeast, wheat, dairy and just about everything else for 3 months. All I could drink was water. I could eat meat and veg and rice and that was about it.
After 3 months more tests were done, and pollen/grass had shot up to 75-80, and everything else had been cleared up. These low-level allergies, especially to yeast, build up over a long period of time (
http://en.wikipedia.org/wiki/Candida_albicans) which affect mainly the immune system.
Since then I've watched what I eat, so moderate intake of sugar, yeast, alcohol, etc. and have been hayfever free ever since.
A small price to pay I feel, and I'm sure any other sufferers would probably agree.
No need for drugs which merely mask the symptoms and don't treat the causes, and after a while the body builds up a resistance to these drugs anyway and you need to buy more and more or go and get something daft done like a steroid jab.
If anyone wants details, feel free to PM me and I'll see if there's a practitioner near you who you can contact.