I identify with lots of your symptoms, heart beat issues, fogginess, weak / numb hands, muscle twitches, pain in joints, tired, irritable ...BUT I have only just had the Mirena put in 2 months ago and my symptoms have actually got better not worse.
Have you had your iron levels tested? How stressed are you? What are your progesterone levels like? I too had more problems after my second child and had a copper coil between my two children as birth control which caused heavy periods and hence anemia. I am convinced that it is the low Iron combined with stress that casues the symptoms.
I do hope you feel better soon. There are lots of women including my self that are dealing with this overload of stress in such a busy world....we were designed to look ater bablies and pick fruit, not rush areound 6am till 10 am everyday with 101 things on our mind.