Meghan Trainor Gets Candid About Falling Off the Fitness Wagon -- and Getting Back on Track (Exclusive)

The pop star admits that keeping the weight off has been a challenge, but fiance Daryl Sabara has helped her along the way.

Meghan Trainor is still working on her fitness! 

The 24-year-old pop star hilariously claims that her new, healthier lifestyle stems from a desire to "live forever," but admits that keeping off the pounds has been challenging. 

"I did fluctuate and learned that the quick way, 'cause I never ever lost that much weight before," she tells ET of her recent 20-pound weight loss. "I immediately noticed, like, 'Oh, there's a ten back' and then I had to lose it again. So that's a lesson to learn." 

But for Trainor, it's about more than just what the scale says. 

"I just want to live forever, man. I wanna stay looking young forever," she quips. "I stopped drinking, stopped doing anything bad to my face. I don't want to deal with acne anymore -- I'm 24, I'm over it, and I just want to live 'til I'm 106." 

By her side is fiance Daryl Sabara, whom she still credits with keeping her fitness on track. 

"He really changed my life. He showed me how working out can be fun. I didn't believe it, but now it's true and it feels so good when you're sore -- I love that feeling now, I'm addicted to it," she says. "He cooks for me and taught me to cook. I never knew how to cook. He taught me, like, secrets how to make your food taste great but also be healthy for you." 

Trainor -- who is currently gearing up to return for the second season fo The Four -- may have that bride-to-be glow, but she hasn't yet made any plans to walk down the aisle. 

"I don't know what we're doing," she says. "I think we're gonna run away or something, but I can't imagine my dad not being there. So we gotta figure it out." 

Time is ticking for the couple, who are anxious to become parents. 

"I have crazy baby fever!" Trainor gushes. "I asked my therapist recently 'cause I walked by, in Whole Foods, the diapers and was just weeping. Just crying, and was like, 'What's wrong with me?' 

"My mom had babies at my age, so I think it's just in my blood," she reasons. "It's in my family -- supposed to pop them out right now. But I'm gonna take my time, I'm gonna do this career."

In the meantime, Trainor expects to put out her third studio album this summer. She'll also be scouting talent as a judge on Fox's second season of The Four, beginning June June 7. 

For more on what to expect, watch below.