I have been battling with the very same dilemna. I got the Mirena at the End of January. In February, I was diagnosed with Hypothyroidism. I have almost all the same symptoms that you listed... and the weight gain is particularly disheartening because I lost 100 pounds in 2005 and kept it off until I got the Mirena... now I have gained back 35 of the 100 pounds I lost.
Im too tired to exercise. Im too achy to do much really. I have no sex drive. My skin is so dry it hurts in some places. I have acne for the first time since I was 15. Im chronically cold. Im constipsted. Im cranky. I cant consentrate. Going to work is a serious effort, and when i get home, I almost always want to take a nap.
My Dr. said my TSH level is still high, (it was 24 when I started Synthroid) and he is still adjusting my medication... but I had a feeling there was more to it because I simply dont feel any better... and he said I should be experiencing some level of relief by now.
I am so glad to have found someone with a parallel experience. It lends legitimacy to what I already suspected.
Please let me know if you find out more... Thank you so much for sharing-