"I've actually been much sicker this pregnancy than the other two. I have been nauseous for three months straight," the 37-year-old Oxygen reality star tells the new issue of Us Weekly (on stands Wednesday). "It's starting to get better now thank goodness. And, I'm showing way more a lot sooner. Guess it's true when they say your body remembers!"
Married since 2006, Spelling and husband Dean McDermott, 44, already have two children together: son Liam, 4, and daughter Stella, 2.
"Liam already kind of knew. He kept saying, 'Your belly is getting huge. That means there's a baby in there,'" Spelling recalls. "When we finally told them they were really excited. Liam wants a brother and Stella a sister. And now they are obsessed with telling people, 'My mommy has a baby in her belly!'"
The Beverly Hills, 90210 alum -- who is due in October -- tells Us she couldn't be more excited to add to her brood.
"It's been over three years since I was last pregnant, so it's like the first time all over again," Spelling says. "So I'm nervous but beyond excited. We always wanted a big family."
For more on Spelling's pregnancy, pick up the new issue of Us Weekly, on stands Wednesday.