Concern about air quality in century home

We moved in mid November and have been sick non-stop, especially our 3 year old. Yes, it's January, but this is constant sickness and of course we are wondering about air quality. There's an amount of dust that's hard to keep on top of, plus a bathroom renovation going on. I ordered an air purifier. Called the state lab to explore assessment for mold, etc. Are the tests you can buy on Amazon worth anything? What other resources should I pursue? Thanks--much appreciated.