Weird bleeding

Okay so a month and a half ago I got an IUD inserted (merena) and recently within the past week my spotting has gotten darker and heavier. This weird awful smell has added onto it and I have no idea what it is. Could someone please tell me what I should do? I don’t know if it’s an infection or what but its getting to the point where I can’t stand it. Also the blood that comes out is super dark and brown. Anyone have an idea or advice?