I was fed a vegetarian diet as a baby and I had terrible springtime allergies and year round congestion.
As time went on, my eating only became more restrictive and my congestion only got worse. I’m mainly a mouth breather and I always have been. Doctors have told me to stop in the past, but I can’t. I just naturally breath through my mouth. I thinks it’s because my nose is so congested
I had the worst nasal congestion when I was on low carb so yes (no allergies though). I would read Newsletter 3. Specifically Danny Roddy on carbon dioxide and all the links in the article.
You can also check out normalbreathing.com although imo that website is kinda messy, but probably its just my browser. I got an exercise from that website I do that quickly opens my sinuses. Normal inhale+exhale that takes 2-3 seconds then pause 2-4 seconds and repeat.