IUD Experience. Please share...I'm nervous about getting my put in...

I have a few medical conditions which prevent the estrogen/progesterone combo bc from being effective. So I need the progestrone only bc and my fiancee and I decided the IUD would be best given everything that's going on (quickly approaching our 2nd deployment and I'm going to grad school soon). However, I've heard so many horror stories that I am freaking out about getting the mirena. please share any stories or advice.