Hi I Am A First Time Mom At 42, Now

Hi I am a first time mom at 42, now 44. I have profuse bleeding since the baby however I had a copper iud put in 8 weeks after delivery. My doctor said it was not because of the IUD. I since chandwd doctors and he said the excess bleeding was infact caused by the copper iud. Also my ultrasound showed a 15mm thick endometrium. What could this all mean???