Heavy bleeding with Mirena IUD

I’ve had my Mirena IUD for 2 years and have never really had a period with it. I have had like maybe 3 days every 3-6 months of dark discharge but hardly anything. Never had to wear a tampon or pad. Well I just got done bleeding for 9 days. It was nothing like I have had before. Two of the nights I woke up with blood all over my underwear. Sorry so much TMI! I did take a pregnancy test and it was negative.Does anyone know what could have caused this? I don’t have insurance at the moment so I am trying to avoid going to the doctor until I get insurance again.