What's the humidity levels in your home?

I’m not sure, is there a way to test humidity? We have a half finished basement and keep a dehumidifier running. It hasn’t really kicked on since the colder weather started.

If there is a dehumidifier there, it might be a newer one that has a digital read that shows the humidity. If it hasn't kicked on since colder weather started, make sure it's still running correctly.

You can also get a humidity sensor or few, depending on how large the place is. One upstairs and one in the basement at least. They can be fairly inexpensive dial read, or more expensive digital. They are usually found with either the air purifiers/conditioners/heaters, or sometimes with other indoor thermometers.

You mentioned a particular window- double check that area, inside and out to make sure it's all in correct order. Perhaps consider getting an air purifier for that room.

Also, if the furnace/AC system wasn't cleaned or checked recently, you could be having some leftover ick in the air system. Make sure you change out your furnace filters, get the good filters.