Okay, I had my first Mirena inserted in 2002. I had ZERO issues. Slight cramping and then, miraculously, NO PERIODS until it was removed in 2007! The 5 years was up. I was pregnant in less than a year without it and then after the birth of my son in February 2009, I had another Mirena inserted at the 6 week check up after birth. Since then, ALL of the above relates to me! I found a new OB and she found that the Mirena had been inserted into the wrong spot! Imagine my surprise, now the understanding of the cramping and constant heavy periods. She removed it and put in another ... safest form for me as I am 37 and a smoker. It's been 4 weeks since the new one and now I have that funky brown discharge...its nasty and I will keep you posted once I tt the Dr.
Good luck all and thanks for sharing, at least I know its not just me!