I'm so sorry that you are going through this at such a young age and I know the hell only too well! Please have Mirena removed and don't let anyone persuade you to keep it! You know your own body and well done for making the connection with Mirena, it took me a lot longer. Please let us know how you are doing and come here for support when ever you need it!
I would advise that you take a supportive freind or parent with you when you have it removed.