Hi Greg! I am just now seeing your question, and hope after almost 6 weeks, you've found what you need to help with your allergies! My allergies are bad enough that I take four different prescription meds for them, and take Benadryl at bedtime (and sometimes during the day), as well. One of the Rx meds I use is Flonase. It's available otc, but I can get Rx strength through a mail order pharmacy at no cost. I also use Ipratropium to help with the extra secretions that Mestinon causes, because the extra secretions add pretty significantly to my allergy issues.
I would check any OTC medicine for interactions with MG meds, before taking them, and see how it goes. My neurologist did have me stop taking one allergy med, but unfortunately I can't remember the name of it now. Checking with your doctor(s) is always a good idea, so be sure to let them know next time you talk.
Have a great day and a good week!
❤️ wm