I have just returned from the hospital where I took an allergy test. I've got bad news and good news.
Bad news: Seems I've got no allergies to the common stuff. So the mystery of my stuffy nose is still not solved. :(
Good news: I'm definitely not allergic to cats (and dogs)! YAY!!
In the meantime I've received a stronger nosespray that hopefully helps.
It's still too early to say, but I'm cautiously optimistic about the new nosespray.