Back after baby -- and better than ever!

Nearly two months after giving birth to son Camden, Kristin Cavallari made her first post-baby red carpet debut on Tuesday night in NYC. The 25-year-old new mom stepped out to attend Ulta Beauty's "Pucker Up" event to celebrate their Donate With a Kiss campaign in NYC.

The former Hills star looked stunning and slim in a little back dress for the event and chatted with Us Weekly about how she lost the baby weight so fast.

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"I started working out when he was 4-weeks-old," Cavallari, who welcomed baby Camden with fiance Jay Cutler on Aug. 8, told Us. "Breastfeeding honestly burns 500 calories a day, so that's been very helpful. And I'm a healthy eater in general, so I've just maintained a healthy lifestyle."

And some light exercising has helped too. "I've been on the treadmill and doing a little jogging, but taking it easy and not killing myself. And I haven't really been stressing about it either. I think that helps."

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Despite the lack of sleep, the first-time mom said motherhood is "amazing."

"You really feel like your life is complete," she said. "He puts everything into perspective and makes you realize what your priorities are. Just seeing him smile melts my heart. It's the most amazing feeling."

Hubby-to-be Cutler, who is the 29-year-old quarterback for the Chicago Bears, has been very hands on. "He is a really great dad," Cavallari told Us.

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The busy mom joked she's had to change up her beauty routine since giving birth, but Cutler doesn't mind.

"Honestly, the only time I wear makeup is when we have date night!" she said. "During the day, I don't wear any makeup. But I actually enjoy it. It's nice to give my skin a break, and it's not exhausting for me to get ready in the morning."

"Luckily," she added, "Jay likes me with no makeup on! So it works out."

This article originally appeared on Kristin Cavallari on Hot Post-Baby Bod: I'm "Not Killing Myself" or "Stressing"