All caps are very hard to read. Your house, very likely, is suffering from poor ventilation (air exchanges with outside air) and high humidity. The dark marks on the drywall are very likely to be mold, and it would not surprise me to hear that your family has been suffering from a higher than normal amount of respiratory and sinus problems this winter. Ironically, you spend extra time at home hoping ot feel better, and its the worst place to be.
Even though we all went through a long period of time where the focus of our energy was spent sealing up every nook and cranny in our houses in the pursuit of "Energy Efficiency", we have succeeded, and that is our problem. Try these suggestions:
1. Whenever you take a shower, run the bath fan. 2. Consider installing a whole house fan that both draws air out of the house and allows fresh air in. This should be on a timer, and can be integrated into a central forced air heating or cooling system. In the mean time, leave a few windows open if it won't freeze you out!
3. It is possible that your carpets now host mold and mildew spores. When it gets a little warmer in your area, consider having them professionally cleaned, with emphasis on allergen controls. 4. Your drywall could very well be damaged from the humidity. If this is true, you may even be lacking a vapor barrier behind the drywall, and your exterior wall cavities may be wet and rotting. Pick an area where the drywall is extra dark, and remove it. Check the studs and insulation for moisture and rot damage. You may wish to hire an inspector or contractor to perform this for you, and provide suggestions. 5. Kilz or Binz primer, once you have dried everything out, should effectively hide stained but structuraly sound drywall. Then paint. 6. If you have a crawlspace, high humidity in the home can also be caused by standing water in your crawlspace. This is a serious problem that has been dealt with extensively on this forum. Ctrl-f then "crawlspace".
Keep in mind, I haven't seen your home, and my suggestions are very general and intended to point you in directions you haven't considered. Only by seeing it first hand can a qualified professional or serious do it yourselfer give a qualified diagnosis.