Kristin Cavallari wasted no time losing the baby weight!

The 25-year-old former Hills star welcomed her first child, son Camden, with fiance, Chicago Bears quarterback Jay Cutler, 29, on Aug. 10.

PHOTOS: Kristin's sexy maternity style

Just five weeks after giving birth, Cavallari "has already lost all the weight by working out like crazy with a trainer," a source tells Us Weekly.

Last week, the reality star tweeted, "Walking uphill on the treadmill to work out this booty. Bye bye baby weight."

PHOTOS: Kristin's best bikini moments

While Cavallari has had no problems losing the weight, there is one thing she's struggling to change after becoming a mom.

PHOTOS: Celebrity pregnancies

"Still need to work on my potty mouth," she tweeted on Sept. 15. "Swearing just comes so naturally to me."

This article originally appeared on Kristin Cavallari "Has Already Lost All of Her Baby Weight"