Katherine Heigl on Post-Baby Body, Placenta Pills

New baby, new life! Katherine Heigl and her husband Josh Kelley share the first photos of their baby boy Joshua Bishop Kelley Jr. Subscribe now for the exclusive photos and read why the mom of three left Hollywood – only in PEOPLE!

Though Katherine Heigl says that her first pregnancy with now 5-week-old son Joshua Bishop was “pretty easy,” the changes in her body threw her for a loop.

“What was rough with the pregnancy was just the terror of the weight gain,” she says. “You’re going to gain weight — that’s just part of the whole thing. Stepping on that scale every month in the doctor’s office was heartbreaking for me because I’m used to watching that so closely, and the moment I start putting on weight being like, ‘Oh no, I have to rein it back in.'”

She adds, “I tried to be as healthy as I could about it and not go crazy and go over the top with weight gain, but I still gained a lot for me.”

“I gained like 40 lbs.,”she says. “That’s hard for an actress who’s spent her whole life trying to always lose that last 10. But I’m so grateful for my body right now because I feel like it’s doing what it needs to do.”

• For more on Heigl’s life with her new baby and her red-hot career, watch the full episode of People Cover Story: Katherine Heigl and Joshua Jr., available now on the People/Entertainment Weekly Network (PEN) and at People.com/heiglbaby. Go to PEOPLE.com/PEN, or download the app for Apple TV, Roku, Amazon Fire TV, Xumo, Chromecast, Xfinity, iOS and Android devices.

Breastfeeding has brought on other unexpected physical changes. “My boobs just got so ginormous,” she says. “It was horrifying! I’ve always had fairly large breasts, but [I went from a] DD to an I. Did you know that an I even existed in bra sizes? I didn’t. I didn’t know that until I started having to buy bra sizes in an I. That’s D, E, F, G, H, I — that’s horrifying!”

But, she says, breastfeeding contributed to her post-baby weight loss. “Within a week and a half after he was born, I dropped so much weight, and I was like, ‘Oh my God, my body really does know what it’s doing, I’m just going to back off and not stress about this,'” she says.

“I still have a good 20 to lose, but I’m not going back on camera as an actor for quite some time and I can take my time and do this healthy, and do this slow, and do it kindly to myself and not beat myself up about it.”

Heigl, who worked with a naturopath throughout her pregnancy, is consuming her placenta in pill form. After her cesarean section, “They told me that another mother down the hall had a company that freeze dries pills. This guy came, he was a total cowboy: Cowboy hat, cowboy boots … and a bag of placenta! He took it to his wife who freeze-dried it and turned it into pills and I’ve been taking them.”

For more from Katherine Heigl, pick up the latest issue of PEOPLE, on newsstands Friday.

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