What Causes Pregnancy Symptoms While Having Mirena?

My name is leslie i am a 23 year old female mother of a 4 year old and a 18 month old. I had a mirena inserted in january of 09. I have recently been experiencing breast tenderness, fatigue, headaches and cramping in my pelvic area. I took a home pregnancy test and it was negitive. should i have my mirena checked? could my mirena result in a false negitive? what should i do?