you are using IUD cu T as contraceptive
. mild bleeding that intermensrual bleeding some time is common . but heavy bleeding and pain should not be there .
intensive pain occur when cu t is not properly placed . or very less because of perforation or infection called pelvic inflammatory disease
as u have continuous bleeding this is causing weakness in you .
u should consult to your gynecologist for all complaint .
get whole abdomen sonography
get your hemoglobin
hope this will help u