who's had an IUD removed?! (TMI)

Okay so little back story. Very early and HEAVY period so I've been on BC all my life. Got pregnant ON the pill in 2013 had my son then INSTANTLY without a period went on the mirena 2014. Had some abnormal bleeding and some pain but no big deal. Okay so fast forward two years nov 2016 I had the mirena removed because of a cyst, abnormal bleeding, and constant pains. I am now 4 months off the mirena and since December I have had horrible troubles with abnormal bleeding & I still have the cyst! No periods though. I am bleeding probably 75% of the month and it'll range from spotting while I wipe to full on needing tampons. This week I started spotting like I normally would and yesterday it turned into VERY heavy bleeding. Since 8 pm last night I've gone through a whole box of super tampons with extreme pain. I'm talking like labor pains. My doctor keeps saying "it's okay this is just your first period"  HOW IS THIS OKAY?! Anyone else experience this? Pleaseeeeee help me! I have a biospy scheduled for the 20th because my uterine wall was too thick at a check up ultrasound and I just recently got bloodwork done and I am not pregnant. I know it takes awhile for your body to adjust but I feel like my doctors excuse for the bleeding is a period.. I haven't felt myself ovulate and she KNOWS I'm not ovulating from tests she done. This is driving me crazy.