Since my teenage years I was mildly allergic to pollen, and now in my adulthood it seems to be getting progressively worse. Each spring is worse than the previous one, and the antihistamines do less effect (or so I subjectively feel).
For example taking the right kind of antihistamines, taking them in the evening before bed, and most important regular cleaning.
Personally I only take allergy medication maybe 50-100 days a year, and usually just a half dose. I have definitely heard from people with worse symptoms that they get a tolerance to medications so it may help to switch between them if you take them year round.