Demi Lovator is all smiles nowadays -- but that wasn't always the case!

The singer, who donned a pair of flares and an AC/DC shirt and an army jacket, made her way into a Los Angeles office building as she prepares for her The Future Now tour with Nick Jonas, which begins on June 29 in Atlanta, Georgia.

Yesterday, the 23-year-old talked to Refinery29 about some less happy times, namely when she was battling a substance abuse problem in her teen years. The singer admitted "I was a nightmare to work with."

Recalling how she viewed her family, who was trying to help her, she said, "‘Try to ground me -- I pay your bills.'" The star, who celebrated four years of sobriety in March, also said, "Prior to getting sober, I was one of those people who was like, I don't give a f--k, whatever. And I used that as an excuse to do whatever I wanted."

She admitted the website that wild parties just aren't her bag. "I had to learn the hard way that I can't do parties anymore. Some people can go out and not be triggered, but that's not the case for me."

But that doesn't mean Demi can't have fun -- and we have the Carpool Karaoke to prove it!

Earlier in the week, Demi appeared on The Late Late Show with Nick Jonas's fun-filled segment with Nick Jonas and gave the hunky Jo Bro a hard time about his love life and his purity ring! It's pretty hilarious!