I would also ask how long you have been on the IUD. The weight gain is not always as sudden for people who switch from other hormonal BC methods. They have testified to experiencing a loss followed by a plateau and a return to weight GAIN.
The truth is that over 90% of the 500+ posts on this thread are of people experiencing similar and consistent symptoms. They are of all ages and are genuinely confused by it all. There is SOMETHING legitimate about the complaints just taking into consideration the statistics involved.
Do you notice that all of the women that are gaining weight are in their 40's? HELLO! As we get older our metabolism slows. I have been on the pill for 1 year after I had my daughter and gained 20 pounds. Went on the Copper IUD and have been losing weight ever since. Then again I am only 22 ;-)