– Rihanna's derriere isn't as ample as it once was, and the singer doesn't like that fact. "I'm a size 0—and not happy about it!" she tells Us Weekly. "I went way too far. I prefer myself a bit chunkier. I want my old butt back!" The 24-year-old lays the blame on her crazy schedule, which apparently has her losing out on sleep ... and landed her in the hospital post-Met Ball. "It's harsh on your body!" she says of her jam-packed life. And her run-yourself-ragged approach has many worried she's falling apart. Chris Brown and Drake apparently don't mind the size of Rihanna's booty; click for the latest on their reported bar brawl over the singer.