(Clear Channel)

Yet another former child star has hit a rough patch.  SELENA GOMEZ spent two weeks in rehab last month.


Her rep confirmed it . . . saying, quote, "Selena voluntarily spent time at The Meadows [in Arizona], but not for substance abuse."  They didn't say what she DID go for . . . but the obligatory "exhaustion" excuse is being thrown around.


In addition to drug and alcohol abuse, The Meadows' website says they treat:  "Sexual addiction, codependency, depression, bipolar disorder, love addiction, panic and anxiety disorders, eating disorders, gambling addiction, and trauma."


In the past two months, Selena canceled tour dates . . . said she "needed to spend some time on herself" . . . and allegedly toldJustin that HE needed to go to rehab.


A so-called "source close to Selena" tells Radar Online that, quote, "She'd been partying very hard."  Supposedly, she was drinking, smoking pot, and had begun "experimenting" with prescription drugs like Xanax and Ambien.


Meanwhile, TMZ claims Selena is also addicted to . . . JUSTIN BIEBER.  She'd started hanging out with him and his buddies again around the New Year, and her people thought he was a bad influence . . . so they encouraged her to go to rehab.