'JT' is right. You need to remove the cause of the moisture and either increase/decrease the wall/room temperature.
For now, once you clean off the mold and mildew, I suggest you use a primer that will, basically, seal the wall. Stain-Kilz is a product that is very noxious but very effective. Be SURE to have good ventilation to the outside. Open the apartment door and put the fan in the window where you're working and have it blow outside. No joke, it's heavy. Then, you need to buy a good paint that contains the addatives to prevent mold and mildew. You'll pay upwards of $25-28 per gallon but it's worth it. Don't skimp on cheap paint or you'll be back painting. The primer is one coat and I suggest 2 coats of finish paint. Of course, you'll have to do finish painting on all 5 'walls' so they all match. Try Finneran & Haley if they're in your area. Again, read the contents for the addatives (or you can buy the addatives separately to add to the paint as you need it), and don't be cheap.