Worth a mention. I had two IUDs - first one was fine but when I had the second one I had all sorts of issues like pain and bleeding etc. Various scans didn’t show anything untoward and they tried to tell me everything was fine when it blatantly wasn’t - I was in so much pain and kept randomly gushing blood out of nowhere! Eventually I asked them to take it out and all the symptoms stopped… years later I find out that I had adenomyosis the whole time and that the IUD was probably poking into an area of it and causing the symptoms.
Bottom line; the odd bit of bleeding here n there can be normal but if it happens a lot and/or you’re getting pain and don’t feel right, persist until they do something! If you don’t think it’s right then you’re allowed to say so - they’d’ve just left mine in if I let them so follow your instincts xx

When i was on prolonged bc (not iud) for 8 years straight, it made my period pretty much go away completely. Id have light spotting every few months or so. Until it came back. It came back thick and brown/black sludgy. Has been this way ever since 5+ years now. Anytime i ask about it, my gyn says it's normal but i really don't believe that. I use to have really heavy long periods before that birth control. I don't know if my period classifies as heavy anymore but it is nasty. I would like to think a good gyn would be open to listening to your concerns about your period change. Mine was not. I would still ask about it anyway and do your best to explain why it doesn't seem normal especially if you're certain it's not a period.