I wish I had advice to offer, but I was going to post almost the exact same problem! We have a four year old house in Massachusetts with water spots all over our ceilings. Now I am afraid that we are getting mold and structural damage from the soaking the underside of our roof gets every winter.
We have tried to eliminate every possible source of air leaking into the attic. We have added another layer of insulation (which is now completely soaked). We have a continuous ridge vent and continuous soffit vents. The original insulation is paper backed on the side facing down which should be an adequate vapor barier.
Are we keeping the attic too cold? Do we need a better vapor barier? What sort of contractor could troubleshoot this for us? Our original builder and the town building inspector have exhausted all of their ideas.