Re: light-headed / Dizzy
Yes, most likely its the Mirena. I had mine put in Sept. 2006 and had the same symptoms you describe start 2 months later. They never went away, just got better and worse (sometimes I had such bad vertigo I was convinced I had a brain tumor!) I had bloodwork done twice, once was 4 months after insertion and once 17 months after insertion. Both found nothing abnormal, neither doctor was willing/thought it appropriate to do any more tests.
Get it taken out. I had mine out almost two weeks ago and all these symptoms (and more) are gone. I felt clear-headed for the first time in the nearly two years I had it almost immediately after it was out. I no longer get dizzy, lightheaded, suffer from extreme fatigue, etc.
Worst case scenario, you get it taken out, and either discover it was the Mirena because you feel better or it wasn't the Mirena after all. Still, a non-hormonal, no foreign object continually in the uterus form of birth control is probably better for you anyway. If you get it taken out and miss it after a few months you can always get another one.