Dark spotting got two weeks straight

So I’m wondering if anyone might have experienced this... I’ve always had super regular cycles (29 days) and I have had a copper IUD for almost two years. I’m on day 15 of my cycle now, I had a normal period- nothing seemed off... but ever since my period ended, I’ve been having brown spotting/discharge nearly everyday. Sometimes it’s heavier/darker than others, but it’s been going on since the end of my period around day 5-6 ish. Any ideas?