The 'Not Fair' hitmaker – who has previously struggled with her weight – is concerned about shedding the pounds after she gives birth to her first child.
She said in an interview with Britain's Grazia magazine: "I still think I'm fat. Right now I'm worrying about how I'm going to lose weight after the pregnancy. I feel like an elephant, but I do get the occasional sexy pregnant day where I think I look great."
The 25-year-old star has also revealed she wants to marry boyfriend Sam Cooper but is too busy focusing on her pregnancy and new fashion store Lucy in Disguise.
Lily – who is taking an extended break from her pop career - explained: "Of course I want to get married but having a baby with someone is way more important and we're both really excited.
"The idea was to get Lucy up and running and then get pregnant but it all happened at once.
"I can't say this isn't terrifying because I'm taking a massive risk. I'm turning away from something and focusing on Sam, my baby and my business but that's what I want."