Have you verified the duct work runs to the exterior of the home? Length of pipe? What is the CFM rating of the fan and is it adequate for your room.
For rooms with 8' ceiling: Room Area (Square Feet, widthxdepth) x Constant (1.07) = Cubic Feet Per Minute (CFM) needed
Other ceiling heights: Room Area (Cubic Feet, width x depth x height) x Exchanges (see below) = Cubic Feet Per HOUR. Now divided by 60mins = Cubic Feet Per Minute (CFM) needed.
EXCHANGES: Bath 8 Kitchen 15 Laundry Room 6
There is another discussion going on VERY similar to yours :) http://www.hometalk.com/activity/117779
Patti, before you paint, wipe off the condensation streaks with a damp sponge so they do not show through the new paint.