By Chloe Melas, CNN

(CNN) -- Demi Lovato is experiencing "complications" and remains hospitalized following her apparent drug overdose, two sources close to the singer tell CNN.

Those complications include "nausea, vomiting and a high fever," the sources say.

Although she's expected to "make a full recovery," there is "no estimate" as to when she will be released from Cedars-Sinai Medical Center in Los Angeles.

"[We are] taking it day by day," one of the sources said.

No information has been released regarding what led to her hospitalization.

There had been reports Lovato overdosed on heroin, but a source close to the singer denied that.

Last week, a source with knowledge of the matter told CNN that Lovato plans to seek drug abuse treatment following her release from hospital care.

CNN previously reported that Lovato's family and her former boyfriend, Wilmer Valderrama, have been by her side since her hospitalization one week ago.

At the time of her apparent overdose, a representative released a statement saying Lovato was "awake and with her family."

"Demi is awake and with her family, who want to express thanks to everyone for the love, prayers and support," said the statement from Lovato's representative. "Some of the information being reported is incorrect and they respectfully ask for privacy and not speculation as her health and recovery is the most important thing right now."

Lovato has been open about her struggles with an addiction to cocaine and alcohol, as well as mental health issues and an eating disorder. She also sought professional help for substance abuse and entered rehab in 2010.

"You just have to take it one day at a time; some days are easier than others and some days you forget about drinking and using, but for me, I work on my physical health, which is important, but my mental health as well," Lovato said, adding that she was seeing her therapist twice a week. "I make sure I stay on my medications. I go to AA meetings. I do what I can physically in the gym. I make it a priority."

In the hours after news of her hospitalization broke, fans of the singer took to social media with the hashtag, #HowDemiHasHelpedMe to talk about how she and her music have helped them with their own struggles.

Lovato released a single in June called, "Sober" in which she revealed she had relapsed after six years of sobriety.

"I'm sorry for the fans I lost who watched me fall again," Lovato sings on the track. "I want to be a role model but I'm only human. I'm sorry that I'm here again. I promise I'll get help."

Lovato has been touring and promoting her music in recent months.

She last performed July 22 at the California Mid-State Fair in Paso Robles, California.

CNN has reached out to Lovato's representative for comment