Supposing that it's not a leak, you have to put the vapor barrier on the outer part of the house, not the inner part (because keeping moisture out of the wall area is the idea). This problem often comes from having air conditioning inside, and high humidity outside.
If it also gets cold in your area and you spend lots of time indoors, you may need another vapor barrier on the inner part of the wall- again, to keep moisture out of the wall. Paints can help with moisture, but you would need to paint the exterior of the house in this case (unless you have more recent construction, indicating materials like tyvek were used- then you might want to check the roof for leaks).
For what it's worth proper moisture barrier would really depend on your location: Understanding Vapor Barriers