I know I'm coming in late...but thought I would share with you my experience--
I'm on my 2nd Mirena. I had one for four years, and had it removed to determine if it was the source of some abdominal pain (it totally wasn't) About a year later, I had the second one put in. Both times, my body took a few months to adjust cycle-wise, but I've found that my hormonal responses sort of leveled off, (far less PMS ups & downs) I have a period for about...oh, five minutes or so, and I did not experience any weight or skin changes.
Good luck with the ob/gyn next month. Like many things, despite many others' experiences, your body's response to the IUD will be unique to you!