What Causes Loss Of Fat In Top Part Of The Buttocks?

I am a 33yr old female. I was diagnosed with Crohn's disease @13 years ago, after I developed a perirectal abcess, with a horseshoe fistula. I am currently not recieving any treatment, as I am uninsured. I recently noticed the top part of my butt(crack) has lost all of the fat, become sunken in severly. You can see and feel the sacral promontory.I could possibly fit a softball into the indention that has developed. I did lose @60lbs last year effortlessly. A blood test in December showed only that my iron was very low. I do have minor discomfort when I sit for an extended period of time. I am just worried, as I went through quite a bit with the abcess years ago, and am not looking forward to anything like that again. Is this something I should be worried about, or have checked out somehow? is it part of aging or weight loss? or indicative of something more? Any suggestion would be greatly appreciated.