I have been getting white powdery mould on my clothes in my bedroom!

This has been a problem for about 2 years. I have made sure I'm not drying clothes in my room. I have a dehumidifier running constantly and I make sure I have the windows on the latch to get the air circulating better but it seams like. Things like shoes and scarfs that are under the bed or jeans in the bottom of my wardrobe are getting a mould smell and white powder on. My Dad has put a layer of plastic on the walls then polystyrene backed plaster board to eradicate the condensation that was building up from having 3 outside walls to the room with no insulation. I also have the back door to the garden in the room to that is starting to get black mould on. Any suggestions?