What Causes Nausea, Sensitive Stomach, Rapid Mood Changes, Headaches And Heartburn?

Hi. I have had the Mirana IUD for the last two years with no problems or bleeding of any kind. Recently I have been experiencing lots of symptoms that I would consider pregnancy symptoms, such as nausea, sensitive stomach, rapid changes in mood, headaches and heartburn, I even look like I could be showing??!! I have taken 2 standard OTC pregnancy tests and both have said negative. But I know my body, and I can feel something there. I usually have no bleeding whatsoever, and lately there has been slight spotting along with cramping, which is unusual. How common is pregnancy with the Mirena? I m scared to death that if it isn t a pregnancy, then it could possibly be something terrible, like maybe a tumor????? I definitely feel something in my abdomen just slightly to the left of my navel. There is absolutely some sort of rounded knot like bulge. I am a small framed women and workout regularly and feel like I m in decent shape, which makes the knot in my stomach very noticeable. How common is pregnancy with having the Mirana??