Local antihistamine medication is extremely effective.

Usually feel it in the eyes? Eye drops.

Nose? Nasal spray.

Lungs/throat? Inhaler.

My eyes especially, react quite violently, and eye drops provide instant relief. And by administering right before heading out, I can be good for hours.

I also use a nasal spray, though that requires a bit more forethought. If you get symptoms and your nose starts running, that same mucus is gonna prevent the aerosolised medication from getting to the irritated mucus membrane, so it can't be used to relieve symptoms once they start.

Generic Zyrtec has helped me this spring

I wear a single layer cloth mask for running as that's where I suffer the worst. Makes it really hot and heavy but still infinitely better than wheezing the whole time.

I don't really need it for cycling but it's tempting for combating exhaust fumes too.

I use clear biking glasses for long hauls through rain, if I don't, I get headaches because I keep squinting 'against' the rain, and with those glasses I can relax my face more easily. They would also reduce the amount of pollen hitting you eyeballs.

I would recommend using a weather app/service which also monitors the pollen intensity and avoid high intensity days. Im using Breezy Weather from the F-droid app store.

Also nasal spray/eyedrops before or during the ride helps me a lot, just avoid rubbing your eyes with bare hands. I am using a big single-lense cycling glass to protect my eyes, also good against the wind.

I usually avoid taking tablets as they make me feel drowsy (even the non-drowsy ones)

I just learned that I probably have some allergy when I rode along grass field which had some tractors cutting it.

Not ideal on 140km ride.

I take over the counter stuff year-round. Rhinocourt nasal spray keeps everything open and drained, and Allegra does a decent job with the rest. I used to use Claritin, but Allegra seems to work better.

A more long-term approach would be to try to get allergen immunotherapy, if your local health care system allows for it. It's been great for me - I used to not be able to go out during summers, but now I'm completely fine with just one antihistamine pill per day.

Allergy meds, a mask to filter out pollen, only ride on low pollen days?

Get a stretched out lowrider with fat white walls and big chrome spoke rims. It won't help either he allergy but you'll look pretty cool.