BEIJING, March 8 (Xinhuanet) -- She hasn't been in rehab long, but reports have already come to light suggesting Britney Spears is fed up with the restrictive environment.

Sources told US Weeklythe pop singer has been "getting in tons of trouble" since she checked into the Malibu rehab facility Promises last month.

The source said Spears has been cautioned for using her cell phone and has left the facility to shop.

According to US Weekly's sourceBritney is said to be "angry at her family and her manager for pressuring her to enter the program." Britney believes she is "suffering from postpartum depression," the source added. "(She) does not think she has an alcohol or drug problem."

Last week "Access Hollywood" learned Spears has been reading Brooke Shields' book "Down Came the Rain," which discusses the actress' experience with postpartum depression after the birth of her first daughter, Rowan Francis.

"If she's reading my book, I hope it's helping her," Brooke told "Access" recently. "If it's not and she wants to talk to someone, I'm available."

Spears' family is tryinghard to support her. Before shewent into the treatment center, mom Lynne was helping take care of Britney's two children, alongside Kevin Federline. Britney's cousin Alli showed her support of the star, visiting her at Promises last weekend, while Federlinemade a trip to the facility the weekend before, with Brit's kids.

In other Spears-related news, "Access" has learned the singer recently dropped 3,000 U.S. dollars in an online shopping spree. Britney sent her cousin to pick up her new goods at trendy Los Angeles clothing story Intuition.

(Agencies)