Could be a dust mite allergy. House is closed up, and the humidity is good for mites, sadly.
Very possible. I did just change the furnace/air cleaner filter a few weeks ago, hopefully that will help with the dust. I have the kind that you can keep for "up to" a year, but I am going to replaced it twice a year with dogs and cats in the house. The one I had in for about 10 months looked pretty nasty.