'16 and Pregnant' Star Whitney Purvis Shares Emotional Tribute to Son

Whitney Purvis says she'll always hold on to her late son's smallest quirks ... paying tribute to him in a heartbreaking Instagram tribute.

The "16 and Pregnant" star took to social media Tuesday -- the day after her son, Weston, passed away -- and shared a couple pics of them together ... one from when he was just a baby and another from more recently.

Purvis is grinning in both ... holding her son tightly -- and, in her caption, she says these are just two of the memories she will cherish forever.

Whitney writes that she will remember Weston's favorite songs, the phases he went through, his first day of school, the first time she held him and the last time she hugged him ... among a myriad of other experiences she saw him go through.

She adds, "I love you, Weston more than words could ever describe. Rest in peace, my beautiful boy."

As you know ... Weston was found unresponsive in his bed Monday morning at around 7 AM, his stepmother Amy Gosa revealed via Facebook.

Gosa said the family is still waiting on autopsy results ... but, she alluded to health issues which Weston had been suffering from for a while -- including diabetes.

Whitney was pregnant with Weston during the first season of '16&P' back in 2009.

Weston was 16.