What Causes Yellow Vaginal Discharge Along With Abdominal Cramps While On Mirena Coil?

I have had the merina coil In since May last year after having my daughter last March I didn t go back to check if all was ok with it and don t know how to check the threads and don t get periods anymore also noticed yellow mucas on underwear and been getting bouts of cramp that last for seconds any suggestions of what this could be