C.W.
I'm on Mirena also and yes, it feels like my period has been extended and going on and on. It has gotten better and now I'm not spotting very much at all. It does get better, and hopefully it will get better for you too. My period has gotten lighter and easier to manage.
When I hold it and don't use the bathroom right away, I do get uncomfortable and feel a little pain. I haven't felt the pain after urinating though. If it continues or gets worse, I would tell your Dr.