Late to the party, but I got mine 2 years ago, 6 weeks after my son was born. I don't have it for BC, as I'm completely infertile (premature diminished ovarian reserve/premature ovarian failure), but hopefully to keep my endometriosis at bay and keep my lining thin so my hyperplasia doesn't return. My doctor doesn't want me taking pills, as I had some concerning pains in my chest and calves last time I took them, and my mother has a history of DVT and PE after taking BCP.
Nobody told me to take any kind of meds prior to insertion. I don't remember if I felt anything, but I did get a little nauseated - for some reason, that happens whenever I get a doctor poking around in there. She made me lie down for 15 minutes afterward to make sure I didn't pass out or anything.
My periods got significantly lighter. From February until mid-October of this year, I didn't have one at all
Then I had 2 within 3 weeks of each other
All of the ladies in my mom's group on FB who have one report significant weight gain. I actually weigh less than I did before I got pregnant, but I'm a size larger. My recent bloodwork shows my A1C right on the "prediabetic" border, when in the past it's never been higher than 4.9. I have eaten low carb/low sugar for many years before pregnancy, and have not changed that or my exercise routine (if anything, I'm exercising a lot more now that I have a very active, demanding toddler!). If I recall correctly, the paperwork that accompanied the Mirena did say something about certain patients experiencing glucose intolerance, so it makes me wonder.
So basically, I don't care for it, but I feel I don't have much choice. I either look fat and get treated as if I'm diabetic, or I get uterine cancer.