Hi,
Welcome to ehealthforum,
Having cramps and unbearable pain from IUD is not normal. You should consider visiting your gynecologist/obstetrician at the earliest for a thorough evaluation to see if it is in position and also to rule out any other problems. Do not ignore your symptoms. An ultrasound scan and a serum/blood HCG test done will help to confirm/rule out pregnancy and confirm the position of IUD.
Take care.