Jessica Simpson knows the labor of love it can take to produce a full bottle of breast milk — or, as many new moms call it, "liquid gold."

Jessica Simpson and Daughter Black White Polka Dot Dress and Red Bow
Credit: DFree/Shutterstock

Jessica Simpson is basking in the glow of her new-mom achievements!

The singer, actress and businesswoman couldn’t resist showing off the fruits of her pumping labor on Instagram Tuesday, sharing a photo of a full 5 oz. bottle of breast milk for her 2-week-old daughter Birdie Mae.

“This is what success feels like,” wrote Simpson, 38, adding a cow emoji.

The star welcomed her third child with husband Eric Johnson on March 19. She joins the couple’s son Ace Knute, 5½, and daughter Maxwell “Maxi” Drew, 7 next month.

Simpson couldn’t be more excited about the new addition to her family. And now, with the pregnancy behind her, the mother of three is keeping positive as she heals from her cesarean section.

“She had the best attitude about her recovery,” an insider previously told PEOPLE. “She was very excited about having another baby girl. Her older kids were around [the hospital] a lot and doted on the baby.”

Though a close friend of Simpson recently joked to PEOPLE that Maxwell (who weighed 9 lbs., 13 oz., at birth) was “hoping to maintain her record of the biggest baby in the family,” Birdie had her big sister beat as she arrived at a whopping 10 lbs. 13 oz.

Regardless, the pal added that Maxwell is “so in love with her little sister” — as is big brother Ace — raving, “They can’t get enough of the baby. Everyone is very happy.”

Despite woes from severe acid reflux and extreme foot swelling to sciatica and several bouts with bronchitis during her pregnancy, Simpson still remained active in her older kids’ lives while awaiting Birdie’s arrival.

“Jessica loves being a mom and having a big family,” said another source. “Even while struggling during her pregnancy, she volunteered at her kids’ school. Her life is very focused on her family and making it fun for the kids.”

In the days since giving birth to baby Birdie, Simpson’s friend told PEOPLE the former Dukes of Hazzard star has been “feeling good.”

“The baby is doing really well,” added the pal. “Birdie is perfect, and Jessica is savoring every minute. Her family has been back to visit at the hospital and they are elated. They are just soaking it all in.”