'Teen Mom' Amber Portwood -- RELEASED FROM PRISON ... I'm Pretty Hungry

"Teen Mom" star Amber Portwood was just released from an Indiana prison ... almost a year-and-a-half after she begged a judge to put her behind bars ... and now she's ready to eat.

Amber was initially sentenced to 5 years in the big house for violating probation in her drug possession case.

The judge had given Amber the choice of going to a drug rehab program instead of prison -- but Amber decided she would rather serve time than do the program.

Now, we've learned the 24-year-old MTV star -- who began her sentence in June 2012 -- was released Monday morning (only 17 months into her sentence).

We're told Portwood was granted early release due to good behavior, time served and the fact that she completed two unspecified prison courses while serving her time.

She walked out of the prison today wearing a grey sweatsuit ... and a smile ... and says the first thing she wants to do as a free woman is "go get something good to eat."