'Big Brother' Star Amber Siyavus' Daughter Dies from Apparent Suicide

"Big Brother" star Amber Siyavus' daughter has died from an apparent suicide ... TMZ has learned.

Lexi Tomcavage died Monday night in Ohio, and her death is being investigated as a suicide ... according to the Stark County Medical Examiner. On Sunday, Lexi tweeted 3 times about missing her friend who recently died ... saying "i miss you" and "never been like this before."

Siyavus was a houseguest on Season 8 of 'BB' and was known for her frequent crying. Fans gave her the nickname "Whamber." She finished in 7th place.

Amber's daughter, Lexi, was 18.

RIP