I developed a pretty bad pollen allergy around the age of 30. Every spring I had to take antihistamines that helped a bit (not completely), but they made me eit

I developed a pretty bad pollen allergy around the age of 30. Every spring I had to take antihistamines that helped a bit (not completely), but they made me either anxious or sleepy. Then just for fun I made a bet with a friend of mine -- I tried to do a half-distance amateur tri race (1.9k swim, 90k cycle, 21k running) without any carb intake. So I dramatically decreased my carb intake for 3 months or so from February to May. My allergy has completely disappeared and didn't come back for 2 years (despite me having switched back to eating carbs). Then it came back, and I cut back on carbs again. It subsided. Very strange. The problem is that I can't figure out what is helping. Carbs in general? Gluten? Something else? I don't know because it takes 1-2 weeks at least before the effects kick in, so I can't just simply A/B test.