I've had a merina iud in for 2 years some months i skip a period this month i skipped it but my breasts are really sore n full i am defenetly not preg?

Mirena IUD: If there is any chance of pregnancy, get a serum HCG test to be certain (+ or -) : IUD's sometimes get pushed into the cervical canal by uterine contractions, where they are less effective. Another possibility is a delayed twin ovulation, which has twice as much hormone produced, giving more stimulus to breast tissue.

Can happen: It may be premenstrual breast tenderness or a side effect of the progesterone IUD. Limit caffeine, chocolate, may use Motrin 600 mg orally every 6-8 hours after meals for 2 days or so, should subside, if not, contact your PCP or GYN.