Thanks for the query.
With intrauterine devices some amount of disturbance in the menstrual pattern in common.
And usually that will subside soon.
But as you are having continuous heavy bleeding for 3 months, better to consult gynecologist once get examined and go for one ultrasound
If the cause of the bleeding is only IUD, then with your doctor's advice you can go for removal of loop and choose some other method of contraception
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429