I had Mirena put in and I only had pain the first day or so. It felt like really bad cramps so I took a muscle relaxer and took a long nap. I woke up feeling much better. I had some slight discomfort where Mirena was placed but it went away on its own and I have been completely fine since. I didn't have any bleeding or spotting for 8 weeks.
I have used mirena for 5 years and the experiences I had from initial insertion to having it replaced differ greatly. The first time they played it down pain-wise. But the sounding, insertion, and cramping afterwards were so excruciating that I went into mild shock. It was horrible, but I felt better after a couple days and it worked wonderfully for 5 years. So you're case is typical, and don't be afraid of some spotting or heavy bleeding, some nausea, tenderness of breasts, or cramping. It is convincing your body is pregnant, so it will cause side effects.
experiences breasts nausea couple days mild shock initial insertion cramps muscle relaxer few days nap child birth heating pad back pains sick to my stomach