Mirena experiences?

I've been thinking about getting mirena on my next period but I've heard so many negative things about it. I'm only 18 and I would really like kids someday but obviously not anytime soon. But I've read people say it messes with your fertility afterwards. And I've always thought you had to have a baby before taking it but my moms obgyn said that was the old mirena?? Anybody that's had it want to please give me some advice and your experiences with using it???