Whats wrong with me, Could I be prego?

I have been gaining weight. I went from 89lbs to 108lbs in the past 3 months. I felt pregnant a couple days back in march but I got my period.It was about a week late. I am still getting my period but it only lasts about 4 days now. I have a !0 year IUD & went for a check up in May, I weighed 105 then. I have been bloated in my tummy area & it seems to be getting bigger. I took a pregnancy test last month & it came back negative. I dunno what is wrong! I don't feel prego & I'm sick of this bloating!