For most new parents, the first few months with a newborn, while filled with sleep deprivation and middle-of-the-night fretting, is also full of sweetness. But for Sarah Chalke and her fiance, Jamie Afifi, their earliest experiences with baby boy Charlie were more tearful than joyful. Speaking to Us Weekly at the 38th Annual Gracie Awards on May 21 in Beverly Hills, CA, the How to Live With Your Parents star revealed that her son suffered from colic after he was born on Dec. 24, 2009.

"He had colic for the first three months. I did not sit down…literally just carried him for three months straight," the 36-year-old actress told Us. The upside to his need for constant movement? Losing the pregnancy pounds was relatively easily. "That's one thing to do [to lose weight]," she quipped.

PHOTOS: Hollywood kids -- the cutest pictures ever!

The stress didn't stop there, though. At 12 months, Charlie was diagnosed with Kawasaki Syndrome, a rare autoimmune disease that mostly strikes kids under age 5. Because the symptoms -- fever; rash; bloodshot eyes; red, cracked lips; swollen hands and feet; swollen lymph nodes -- are seen in many common viruses, affected kids are often misdiagnosed. (According to the Kawasaki Disease Foundation's website, 25 percent of those who don't get immediate treatment develop heart disease.)

Their experience with the ailment -- and getting it diagnosed correctly -- was so harrowing that Chalke brought their story to Shonda Rhimes, the creator of Grey's Anatomy, in the hopes of educating people about the condition. Rhimes ended up devoting an entire episode to the actress' ordeal and even asked Chalke to star as the mom of a Kawasaki-afflicted boy. The episode aired on Mar. 28, 2013.

PHOTOS: Celebs' mommy must-haves

Fortunately, Charlie, now 3, is happy and thriving — and eating a ton of kale! "I make green juice for him with kale, apple, cucumber, celery and lemon. He's 3, and I've just kind of done it since he was little. I don't know how long it will last…and he will also eat kale chips. I just take kale with a bit of olive oil and a tiny, tiny bit of salt, you don't need that much, and bake it in the oven," Chalke told Us.

And Chalke is laughing again — a lot. "He's making me laugh so hard. I can't believe someone who's three can make me laugh this hard," she said. "The other day he looked so perplexed and really earnest and he asked me, 'Mama, why does shampoo have poo in it?' You could just see the wheels in his mind turning, like, 'What's happening here?' "

This article originally appeared on Sarah Chalke on Son Charlie: "He Had Colic for the First Three Months"