The pop star opened up for a Channel 4 documentary, Lily: Riches to Rags, which follows the opening of her vintage clothing business.
On losing her unborn son at six months last November, Lily said: “It was a really long battle – and I think that kind of thing changes a person.”
She also explained how at the height of her fame she was suffering from bulimia.
“I used to vomit after meals,” she revealed. “It’s not something I’m proud of.”
The 25-year-old singer continued: “But, I tell you what, a lot of people came up to me telling me how great I looked and I’d be on the cover of every magazine.
“I thought I looked good and it was great to be able to try on clothes and feel a million dollars. But I wasn’t happy. I really wasn’t.
“I would love to be the skinniest minniest person in the world but I can’t do that without being unhappy – I like food.”
The documentary, which is set to air next Tuesday, follows Lily and her sister Sarah Owen as they set up their Covent Garden boutique Lucy in Disguise.
It also shows her final gig at the O2 arena last year before leaving the music industry.
She explained: “My idea of hell would be doing [music] in 25 years’ time. I don’t want to be like Madonna – look at her, she’s mental.”
Lily got engaged to boyfriend Sam Cooper, 32, on Christmas Day.