I have a Mirena IUD. I love it! I had it put in at 8 weeks after my second son was born in February of last year, and I've had no issues at all. I, too, was crampy for about a day afterwards, but now, cannot even tell I have one. I certainly do not have a period every month and when I do, it's for maybe a day, a very light day. Every doctor is different, but mine still suggests a second form of birth control after surgery for everyone due to increased fertility. I am going in a week after my surgery so I can get a prescription for the pill. I don't want to take any chances of getting pregnant during the first 18 months after surgery. Also, if you're having RNY, then you have to take vitamins for life, so adding a tiny pill as a precaution is no big deal.