Levonorgestrel
"I had Mirena inserted at 10 weeks postpartum.  There was a little cramping but I've had worse cramping during my period than having this inserted.  I have 2 kids and had c-sections with both.  Only ever got to 4 cm with the first one so they did a repeat c-section w/ the second. I love it. I don't have to think about birth control and I've had it for 4 months now and no problems.  I've recommended it to all my friends."