Hello,
What you are having is metrorrhagia which is a side effect of the IUD. Get it taken out from a gynecologist. To decrease bleeding you can get prescribed Tranexemic acid from your doctor or progestogen to stop bleeding. Also get other causes of metrorrhagia ruled out.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
Has your doctor checked you for fibroids and polyps and all of that? Have you had an MRI of your uterus?