My Hair Has Been Thinning This Past Year, It's Extremely

My hair has been thinning this past year, it's extremely dry and brittle, mostly on the left side of my head. My hair is uneven, the left side is way shorter and breaking off on the ends and so dry compared to the right side of my head. The only thing that had changed was that I had gotten the Mirena birth control put in September of 2015. My OBGYN is saying that the Mirena would not cause this but it's the only thing that has changed. I also had her check my thyroid and the tests came back within normal limits. Please help!