By Selena Hill (staff@latinospost.com) | First Posted: Jan 16, 2013 02:59 PM EST

A very pregnant Jessica Simpson talked candidly about her second pregnancy last night on The Tonight Show With Jay Leno. The 32-year-old singer, fashion designer and reality star told Leno that she was totally shocked to be pregnant again just six months after she and her former NFL star finance Eric Johnson had their daughter Maxwell Drew.

"I was extremely shocked," said the Fashion Star judge. "Because I was going through a lot of hormonal changes, trying to get back to the old, vibrant Jessica. You know, it was kind of like a one-night stand. And it happened, all over again!"

Because of the unexpected family addition, Simpson admitted that she and Johnson had to push their wedding date back, again. They've been engaged for two years. "We've had two different wedding dates, but he keeps knocking me up," she joked. "We're doing it very backwards, I know... I'll just keep my legs crossed, I guess, this time," Simpson added. "Apparently it was a part of God's plan for my life."

Simpson, a spokeswoman for Weight Watchers, vowed to maintain a healthy lifestyle while she's with child. While carrying Maxwell, she confessed to gaining "a lot more than doctors would recommend." She added, "I was really happy to be pregnant and I didn't ever step on the scale. I didn't realize you could gain that much weight that quickly."

After giving birth, Simpson was criticized for putting on extra pounds before she eventually lost 50 through Weight Watchers and a hiring personal trainer.

Watch a clip of the interview below.