I've had my mirena for almost 9 months now and I LOVE it! There has been some very negative stuff posted on this site from other moms about it, but it is a miracle in my book! I barely have a period, just enough to wear a thin pad for about 3 days a month. But I will warn you that after I first got the mirena put in, I spotted for several days and then I would spot randomly during the first few months which was annoying. But about 5 months after insertion, I was totally regular again and it's been so great! I don't think I hardly have hormonal mood swings at all! I've heard some people say it was so painful during insertion, but mine went in very fast and was just a little uncomfortable. The next day I had some cramping and spotting,etc.
Anyway, I'd say that once you get it, you have to allow a few months for your body to adjust to it.
Good luck! I am thrilled to not have to worry about taking the stupid pill everyday!