I have a 3 year old house and I'm starting to question the inside air
quality. The house in in Houston TX and as typical its wall to wall carpet.
No pets, no smokers.

I'm noticing that during the day time my wife and I are fine while at work,
when we get home and get ready to go to sleep, our throats get slightly
chapped. Just enough to cause a cough.

My first thought is the humidity is too low so I bought a humidity meter
form home depot. It bottoms out at 30-35% at night. Is that too low? How
do I get the humidity higher automatically whithout using a protable
humidifier.

I was thinking it was caused by a post nasal drip, but we visited a friends
house and neither of us had this problem while sleeping over there
(Lafayette LA).

We have aired the house out several times with no change.

What sort of air quality testing should I do to determine if I have some
kind of air problem.

dust?, mold? humidity too low?