Pregnancy with Mirena?

So I'm 18 and I had my first child april 18 2010. And about 4 to 5 months ago I had the 5 year mirena inserted and recently I have been expirencing some pain in my lower stomach kind of like mild labor pains almost and my belly had been looking more round and hard and iv been feeling more tired and sleeping a lot more and a little naucious and I'm a little worried I might be pregnant cause of all the symptoms and my belly looks like I am but its hard to tell cause I hadn't lost much weight from my previouse pregnancy and I'm like 160 pounds... And occassionaly I feel like muscle twitches in my stomach is that normal? I even took 2 home pt's and they were negative am I'm just worring about it to much?