The former Nickelodeon star hopped on Instagram to explain why she's looking a little different these days ... explaining why she had plastic surgery on her eyelids.

Amanda says the procedure, known as a Blepharoplasty, removed the skinfolds around the corners of her eyes.

For Amanda, she says the plastic surgery is boosting her self-confidence and making her feel better about herself ... and she says it's one the greatest things she's ever done for herself.

Amanda debuted the new look earlier this month when she released her new podcast, and there were some headlines about a "new look" and she says that's why she's revealing how she went under the knife.