'Bad Girls Club' Star Whitney Collings Dead at 33

Whitney Collings -- one of the early members of TV's "Bad Girls Club" -- has died ... TMZ has learned.

Whitney's mom revealed the sad news on Facebook, writing ... "I am completely broken and will never get over this. Life is so unfair. She was kind with a big heart."

We don't yet know what caused Whitney's death, but we're told she passed Thursday morning in a hospital near Boston ... her hometown. The medical examiner currently has Whtiney's case and will determine the cause and manner of her death.

Being from Boston was a big part of her persona on 'BGC' back in 2008-09 when she appeared on Season 3 of the show ... as you can see.

She was only 21 when she was on the reality series, and was known as a straight-shooter with a temper ... but also for her sense of humor.

However, her time as a "bad girl" was cut short after she was kicked out of the house due to a physical altercation.

We're told Whitney was 33.