Hi,
Welcome to ehealthforum,
Check if the IUD is nearing the expiry and needs a change. Sudden heavy bleeding is not common while you are on the IUD. Do not ignore the symptoms. You should consider visiting your gynecologist for a thorough check along with getting an ultrasound scan done to look at the position of the IUD. A complete hormonal analysis done would help in ruling out any hormonal derangements that could also be responsible for the sudden abnormal bleeding. Get started on treatment as indicated based on examination and investigation results.
Take care.