Mirena often causes irregular spotting in the first few months. But bleeding this prolonged, more than a year after insertion, isn't typical anymore. Needing a tablet each cycle just to stop it points the same way. This usually means the uterine lining or the device position needs review. Your difficulty losing weight is likely separate, since Mirena itself doesn't usually cause weight gain.
Next Steps
Please see your gynaecologist for a pelvic ultrasound to check the IUD position and the uterine lining. A blood count is also worth doing, since bleeding this prolonged can lower your iron levels over time.
Health Tips
If bleeding ever soaks a pad within an hour, or you feel dizzy or breathless, get checked the same day.