'16 and Pregnant' Star Whitney Purvis' Son Weston Dead at 16

Weston Gosa Jr. -- the son of "16 and Pregnant" star Whitney Purvis -- has died ... according to a message posted by Whitney to Facebook.

The former teen mom shared the sad news Monday ... sharing a photo of the two smiling. Whitney has her arms wrapped around her son in the sweet snapshot.

She captioned the photo, "Rest in Peace, my baby Weston. I love you forever, precious. I'll never understand why life has to be so cruel. You'll always be my baby."

Whitney did not share a cause of death in the post ... but, Weston's stepmom, Amy Gosa, also posted about Weston's passing -- telling fans they tried to wake him up at 7 AM today and couldn't.

Amy says they tried CPR and called an ambulance. Paramedics rushed Weston to a local hospital where he was pronounced dead.

The family is waiting on autopsy results, Gosa says ... but, she adds Weston had a number of medical issues, including diabetes.

Weston was born back on April 2, 2009. Whitney was actually pregnant with him when she and her baby daddy -- also named Weston -- were on the show's inaugural season way back in the day.

Purvis lost custody of Weston and her other son, River, in the years since leaving the show ... and, she was arrested last year for allegedly failing to make child support payments.