Since having mirena (levonorgestrel) coil fitted few months ago i've get really bad lumpy and sore breasts and they itch too how can i stop it its unbearable?

You will still get : Hormone fluctuations that cause discomfort. The iud isn't causing the issues, just not preventing them. You could add a birth control pill to regulate hormones and have double level protection, add ibuprofin as needed or perhaps you will get used to the hormone fluctuations causing the pain.

Likely allergic: This is likely an allergic reaction, i would discuss this with your physician as you may need an alternative form of treatment. In the mean time you can take Benadryl (diphenhydramine) for the allergic symptoms.