What can happen if your uterus is comming down low due to poor muscle control and the dr put mirena (levonorgestrel) in? I'm having a lot of pain 

2 different issues. The uterus coming down too far is a problem with physical pelvic support. It is partly genetic, but is more common after you have had multiple vaginal births. There are a lot of different ways to fix this problem. The Mirena (levonorgestrel) iud placement and cramping is probably unrelated and should be evaluated with an ultrasound just to make sure the iud is still in the right place. This improves over time.