DragonFly,
My doctor told me not too take Benadry daily cause it DRY'S out the NASAL PASSAGES, Plus Dry up all the mucous in the lungs that make it harder to cough up. ( that is what I heard) Asthmatics definetly have more mucous than that of people without Asthma. (doctor told me)....
Personally, what helps me is nasal moisturizer spray. (OCEAN) Anything that says moisurizer for your nose. I don't know all the names of them. Sinus Rinses also help. Buy Sinus Rinses at drug stores or Pharmacy and they can be really helpful also.. Brandi. 
Asthma
Chronic Sinusitis
Chronic Rhinitis