Allergies are a tricky thing, but I'll tell you my story in case it's useful to you.
I suddenly developed allergies with the typical hayfever symptoms. I believe mine were triggered by stress. However, I recently discovered that I am suffering from food intolerances, and as I researched to find information about it, I learned that not only were my allergies caused by food intolerances, but so were all the illnesses I have ever had in my life (anxiety, depression, sinusitis, ear infections as a child, etc).
My body was struggling to cope with the bad food I was eating, and kept throwing different symptoms and illnesses at me (including hayfever allergies) until I finally realised what was going on.
Maybe it would be useful for you to look back through your medical history, and perhaps consider that your situation could be similar to mine.