Jessica Simpson Reveals She Took Diet Pills for 20 Years After Being Told to Lose 15 Lbs. at Age 17

Liz McNeil

On her 17th birthday, Jessica Simpson flew to New York City to audition for Tommy Mottola at Columbia Records.

She sang “Amazing Grace” and wowed him with her big voice. He offered her a record contract. And then, as she writes in her upcoming memoir, Open Book, excerpted in this week’s PEOPLE, he told her: “You gotta lose 15 pounds.”

“That’s what it will take to be Jessica Simpson,” he said.

The singer, who is 5’3″, weighed 118 lbs. at the time. “I immediately went on an extremely strict diet, and started taking diet pills, which I would do for the next 20 years,” she writes.

RELATED: Jessica Simpson Reveals in Her Brave New Memoir: ‘I Was Killing Myself with All the Drinking and Pills’

Jessica Simpson | Mike Rosenthal

As her singing career took off and the pressures increased, she recounts, “I started to hear voices when I was alone at night, waiting for the sleeping pill to kick in…”Do more sit-ups, fat ass.”

In the years that followed, Simpson’s body was scrutinized at every size. Whether she was praised for her rock hard abs (and curves) as Daisy Duke for The Dukes of Hazzard movie or castigated for wearing “mom jeans” at a 2009 concert in which her figure (then a size four) was dissected from every angle.

“We all see our flaws, and mine were just there for the world to rip apart. They weren’t even flaws! They were made into flaws that I didn’t even know I had,” she tells PEOPLE. “It’s insane what can make a headline.”

Jessica Simpson in Dukes of Hazzard | Warner Bros/Kobal/Shutterstock

RELATED: Jessica Simpson Decided to Quit Drinking After Realizing She Couldn’t Dress Up Her Kids for Halloween: ‘I Need to Stop’

Last year, she surprised her fans when she posted on Instagram she’d lost the 100 lbs. she’d gained with her third pregnancy with daughter Birdie, now 10 months. (It’s something, she says with a laugh, that runs in her family. “We all get big pregnant.”)

Jessica Simpson

Now sober for over two years and hoping to help others, Simpson is at peace with who she is. “When I work out, a lot of it is to release anxiety — that’s one of my tools for sobriety,” she says. “Just going walking and talking with my husband.”

“I just thank God that times are changing and people are standing up for themselves and not making it about body image,” she adds. “I hope I can be part of that change and that my daughters will grow up in a world where they can accept themselves at any size.”

RELATED: Jessica Simpson on First Love Nick Lachey: ‘We Got Crushed by the Media and by Ourselves’

Jessica Simpson | Mike Rosenthal

She’s turned her experience into a deeper understanding of her customers while designing the Jessica Simpson collection.  “I can dress anybody there is because I have been every single size,” she tells PEOPLE.

And she admires women such as Lizzo and Ashley Graham who’ve made such an impact. “I’m happy they are able to be there for women,” she notes. “Growing up, we all looked up to fashion models on the cover of magazines. Now that fashion models are plus-size, that is a beautiful thing. I think it’s important as a public figure to show that you’re just like the person who lives next door.”

Simpson is releasing six new songs, along with her audiobook, on Feb. 4.

RELATED: Jessica Simpson’s Memoir Reveals John Mayer Said He Was ‘Obsessed’ with Her — and How She Feels About His Sexual Napalm Comment

Jessica Simpson's Open Book | Peter Zambouros

For more from Jessica Simpson and an exclusive excerpt from Open Book, pick up the latest issue of PEOPLE, on newsstands Friday.

If you or someone you know is struggling with addiction, please contact the SAMHSA substance abuse helpline at 1-800-662-HELP.