What could it be???

I have a IUD in and my periods haven't been normal since I got it two years ago. Sometimes I'll have a normal period and have cramps somewhat heavy bleeding and then other times I'm not even sure if it is my period bc the flow will be spotty and the color is like a brown if not darker and like right now it's like a brown color but the texture is like mucus... What is the deal!!?!? Anyone else have the same things happen? And as far as smell it smells normal... Like a vagina! Lol not fishy or unpleasant...