What Causes Heavy Bleeding & Clots During Menstruation?

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I've had mirena for almost nine months now and for about three weeks I've had heavy bleeding off and on with some small blood clots, and I've also had bad cramps and lower back pain. My breasts have been pretty sore, I've also noticed a small amount of nipple discharge a few times and the small bumps around my nipples  have become larger as if swollen. And for the last week or so I have either been or felt sick in the morning and before bed everyday. Please help with what this could mean!