I'm 43 had a mirena (levonorgestrel) coil fitted 4 months ago had cramps and clots and bleeding frequent , what could be wrong please?

Bleeding on Mirena (levonorgestrel) is highly variable.: Most bleed and spot for the first few weeks and then periods dramatically lighten with 50% not having a period by 1 year. There is wide variations in the bleeding pattern typical of Progesterone only methods. Irregular bleeding is expected and does not mean the iud does not work. If you are concerned please schedule an iud check with your obgyn.