There generally isn't really a lot you can do if you're stuck right in the middle of a forest, full of pollen/animals/insects you're allergic to!
This is more for hayfever sufferers, but there are some obvious simple solutions are covering your face with a dustmask/bandana to keep pollen particles out, but this won't help your eyes.
Three 'natural' ways of reducing the effects:
1)Try and keep your eyes and nose wet - regularly splashing water on your face will wash away a lot of pollen. Another way to achieve this is to try and eat things that naturally make your eyes/nose increase mucus production, or that make you sweat. Garlic and ginger are good examples of suitable foodstuffs - and ransoms (wild garlic) works very well for this in the wild.
2) Make up a wash for your eyes/face - something that will reduce swelling and inflammation - elderflowers, chamomile, yarrow etc are all good for this. When I've had a long day at work, and my eytes are sore, I find boiling a mug of water, adding a tablespoon of elderflowers, leaving it to go cold, and then washing my eyes with this helps a lot. I've used the same thing for friends with hayfever, and they've all said it offers good temporary relief.
3) Try to increase your contact with the allergens - this is most useful if you're allergic to something, and have no way of getting away from it. Consumption of allergens (i.e eating them) is one of the best ways to reduce your reaction to them - and for this, wild honey and flowering parts are good sources of allergens. Eating these regularly over a period of 1-2 weeks will have a significant effect. I have been informed that people with allergies to cats/dogs can help reduce this by making an infusion or tincture of freshly brushed fur and drinking this 3 times a day for 2-3 weeks - however, I've not yet met any one who fancies the idea of catfur tea! (although, knowing bushcraftuk, someone will already be boiling the kettle
) No idea if eating wasps would have the required effect either...
I think for serious allergies that can result in anaphylactic shock (bee/wasp stings being the most common) then the only solution is to always carry appropriate medical treatement, or be very very careful if you don't have this with you!