Very possibly no air circulation. The room needs heat vents and a cold air return. Doors need to be left open until you get that done. I see condensation marks on the walls too. Get some bleach on a cloth and wipe down those walls and get that off there. It appears to be mildew. Leave doors open, and call an HVAC company to get vents installed in there.

Yep, heating absolutely makes a difference.

I know that a lot of older homes don’t have heat vents going upstairs, or that it’s easy to have it installed. You just need to make sure to keep the door open and/or have a fan circulating air. It can also happen in the summer.

If that's an exterior wall, be sure to check for ice dams.

There were ice dams (just found out what that was yesterday-first time home owner). I have called a couple roofing companies, just waiting to hear back to get someone out here to look at it. For now i have the ceiling fans on and a dehumidifier running, the humidity in most of the house is around 45-50% and in this room was 70%. We have been keeping the door shut because it is so cold in there with no heat vents. The other two rooms upstairs have vents so not sure why this one doesnt lol.

Ya, a lot of people are having ice dams this winter. Thank goodness it doesn't happen every winter. You might want to get a heat coil for the gutter outside of the bedroom. We have one in the gutter and down spout outside of our living room we plugged in this year. My daughter is going to get one. She has water from a ice dam running down one side of her house and going into the basement.