Platelet -- excellent explanation!
You -- due to your dust allergies - do you also have a dust mite allergy?? If so - have you gotten protective covers on your bed, bedding, pillows, etc? If you have carpeting in your home, that will be difficult as the mites love carpeting.
Regarding the testing - I have been tested once every 3-4 years, and the allergies change all the time! I have gotten some new allergies as I get older. I was never allergic to cats, now I'm allergic to both cats & dogs! You should really be tested again since it's been 20+ years.
Allergies are caused by a reaction to your immune system. If you have a cold, your immune system will recognize the bug and fight it off. What happens with allergies, is that your immune system gets confused and sees plants or dust as an invader and starts to react, causing all of your symptoms. Allergies are auto-immune, meaning your immune system is attacking yourself.
I read your other post. So you aren't getting allergy shots or sublingual drops?