Sounds like you have to ask your doctor as it could be a function of the IUD?

"Less than 5% of Mirena users may experience:
Vaginal discharge
Breast pain or tenderness
Nausea
Nervousness
Inflammation of cervix, vulva or vagina
Pelvic pain during your period
Back pain
Weight increase
Decreased sex drive
High blood pressure
Pain during intercourse
Anemia
Unusual hair growth or loss
Skin irritations (such as hives, rash, eczema or itching)
Feeling bloated
Swelling of hands and/or feet
Expulsion"