Crazy Bloating.. Look 4 months

So i've had a baby before. I was unaware of the pregnancy until the 6th month so i'm sort of freaking out. Im on Mirena, and have taken a pregnancy test that shows a very clear negative. Yet i'm so bloated it's disgusting. I thought maybe i was gaining weight (and i have, for sure) but my belly looks so bad. Any ideas on what could be going on?