I got Mirena 8 weeks after my daughter was born, March 3rd. The only thing that hurt about the insertion was when the doctor put the clamp on my cervix. Everything else I didn't feel a thing. I also took some Motrin before I went because I was super nervous. Afterward, I had cramps that felt like mild contractions. Nothing too bad. The only thing that bothers me about Mirena, is I've been spotting ever since I got it. It gets heavier when I work my abs. As far as losing weight or gaining it, I'm breastfeeding and it's always been a struggle with me to lose weight until I wean.