Confusing Allergy Test Results

I was diagnosed with asthma about eight months ago. I've been bothered by dust (sneezing spells, runny nose, itchy eyes, etc) for years, and now dust is a major asthma trigger for me as well. I can't sweep, dust or vacuum, or really do anything that stirs up house dust, without setting off my asthma. I've started pre-medicating with my reliever and wearing a mask while cleaning, which helps a lot, but I still find I have to be careful.

I had a skin prick allergy test for the first time a few months back.
It came up positive for ragweed, but negative for dust, mold, dander and all the indoor allergens. I was very surprised, as dust affects me far more than ragweed ever has, especially with my asthma.

Does anyone else have experience with this? Can you get a false negative on an allergy test? Is it possible to react dust as an irritant rather than a true allergy, the way some people react strongly to smoke or fragrances?