What Causes Intermittent Spotting After IUD Placement?

i am 22 yrs old and have been on my period for more than a month now, i have had a recent IUD placed in august. I have gone to my gyn and she precribed me premarin. The weird thing is I spot during the day or sometimes its gone and then at night it will come back. Ive been doing research, but there are so many causes.