'Teen Mom' Star Amber Portwood -- Back in Jail

"Teen Mom" star Amber Portwood is back in an Indiana jail cell ... after prosecutors claimed she LIED about having a medical condition to get out of her weekly drug court appointment.

Law enforcement sources tell TMZ ... Portwood was a no-show at drug court last week ... after telling officials she was on doctor-ordered bed rest following laparoscopic gallbladder surgery. Our sources say Amber's attorney told the court she was ordered to remain in bed for 2-3 weeks.

But here's the rub -- we're told Amber's case manager didn't want to take Amber's word for it ... and spoke to the doctor directly ... who called B.S. on the reality star and insisted she WAS well enough to attend her court obligations.

Amber was immediately hauled back to jail for missing the appointment -- and we're told she's expected to stay behind bars for a couple of weeks ... until a judge decides what to do with her.