Had the mirena (levonorgestrel) coil fitted 3 weeks ago have had tummy cramps on and off, today it is excruciating will this settle and how long.?

It should. Try naproxyn or ibuprofin regularly, go up by 50% of what's on the recommended dose, 600 mg ibuprofin every 6 hours at 600 mg if not a problem. It should pass, maybe u are going on your cycle? If persistant, have a fever or needing to pee increases, see doc. Good luck.