Allergies can develop at any time to any protein, so they're completely unpredictable.
Try taking a low dose of fexofenadine or other antihistamine medication that lasts. Diphenhydramine (Benadryl) is very short-lived (they say 4hr, but for me 2.5hr).
I DO seem to have a super-liver, capable of complete regeneration after total failure, but still, few medications seem to work more than 75% of the duration they claim.
I take 1 Kirkland fexofenadine (slightly weaker than Allegra) and alternate days with .5 pills.
It works without drying me out.
Do what works for you and lots of molds can cause this, not just black mold. Black mold is just another mold, but due to hype, in the Midwest it's practically a swear word.