Jen Affleck’s pregnancy must-haves — and rules for Zac with baby #3

Three kids under three and a nationally televised dancing competition to film? Jen Affleck has her plate full.

The “Secret Lives of Mormon Wives” star is just nine weeks postpartum and gearing up for her “Dancing With the Stars” debut — so while some things remained the same as when she had her first two babies, others were a bit different this time around.

The 26-year-old shared her pregnancy must-haves with The Post, plus the way Zach is making sure she gets more rest since giving birth to their third.

Jen’s must-have No. 1: self-care

Jen shocked fans when she pulled out of filming “The Secret Lives of Mormon Wives” partway through Season 2 — but she says that during her pregnancy, it was important to prioritize “taking time for myself.”

That included exercise but also resting — and “not being hard on myself for that.”

“Also working less and not feeling bad about that, because I think it’s so important to listen to your body,” she said.

“Having babies is a beautiful thing, but it’s also one of the hardest things you’ll ever do. And I feel like as moms, if you don’t take that time for yourself, it’s actually a disservice not only to yourself but to your kids. It’s important to be able to do that in the best way possible, and in order to do that, rest is important.”

Jen’s must-have No. 2: a pregnancy pillow

“I could not live without that,” she said. “Rest is important during pregnancy, so a pregnancy pillow … helps you get comfortable at night.”

Jen’s must-have No. 3: Bio-Oil

The mom of three’s starring in a new campaign for Bio-Oil, which makes products to reduce stretch marks and scars — and says she used it morning and night through all of her pregnancies.

“I definitely think it helped not only hydrate my skin, but I think it also helped prevent me from getting stretch marks,” she said.

Jen’s must-have No. 4: dancing

It’s no wonder she’s on DWTS — moving and grooving is part of Jen’s happiness recipe.

“Dancing, dancing with my kids, dancing a lot. I do that a lot,” she said.

Jen’s must-have #5: moderation

“I think balance is everything, and so I always try to make that my focus,” she said. That means exercising and eating healthy — but not going crazy.

“I try not to obsess over specific things, whether it is work or what I look like or diet,” she said.

Zac’s daddy rules

Home life is a bit different since baby Penelope — or Penny, as Jen calls her — was born on July 2. With their first two kids, Nora and Lucas, Zac was in school — but this time he’s home, and it’s on him to handle kid duty first thing in the morning.

“Because he was in school with my first two, I didn’t have that luxury [to sleep in] — I was basically in survival mode, I basically had to do everything. But because he wasn’t in school with the third baby, I was like — you take the morning shift,” she said.

“And it’s still that way. He knows I’m gonna be up at night and I’m not gonna get the best sleep being pregnant and postpartum. So he takes the morning shift, makes breakfast, does all that, and I get my beauty sleep.”

She doesn’t sleep late, per se — the kids still ask for her — but some days she’s able to get in a few extra winks.