How Should Amenorrhea With Spotting Be Treated?

madam i have an IUD in me from a year. but since three months i have not got my menses, i checked with preg card but im not pregnant. i even had an ultra sound but it showed no abnormalities detected. in the past two months i had spotting at the date of my period but this third month im having spotting almost everyday. its either pink or dark pink or brown, its happnening form 3 weeks! what do u thik is the problem?