Mirena IUD

I’ve had my mirena IUD for 4 years now (for regulating heavy periods) . I had regular periods for the first few months, a miscarriage 7 months in, a few periods after that, then nothing for every 3-4 months (only spotting for a day or two) . Up until 4 months ago when my period came back regularly again. Not heavy but severe cramping. Does anyone else have experience with this? Do I need a new IUD? My gyn swears I have another year on this one, but it doesn’t make sense to go from 3-4 months at a time with just spotting to light periods again every month with severe cramping.