I've had the Mirena IUC since Nov. 2007, and had irregular bleeding up until February '08. February was when I had my last normal period. Since then I have not had a period or spotting. Last week I noticed that my breasts felt sore and I was cramping. They don't feel heavy or swollen and my nipples don't hurt. They just feel sore. I had a tiny bit of spotting last week too.

I have not been able to feel the strings on the Mirena since it was inserted but now I am just freaking out and hoping I am not pregnant. I took two pregnancy tests this past weekend and both were very negative.

What are the chances that I am pregnant, or could it be that my body is just trying to have a period?

Well, mirenas are effective, but again, there have been cases of pregnancy while on the mirena. As far are the soreness + cramping, your worrying alone could cause more pregnancy symptoms... I know it's weird, but it does happen.

You said that you'd already had 2 HPTs and both were negative. As long as both of them were used properly according to instructions, there's a good chance that you're not pregnant. I suggest getting 100% confirmation by going to the doc and getting a blood test panel done.