04/24/2007 AT 03:45 PM EDT
Tori Spelling was thrilled to welcome son Liam
last month – but she wasn't so happy about the weight she put on during her pregnancy.
"I gained 40 lbs.," the Tori & Dean: Inn Love
star, 33, tells Entertainment Tonight
. "Ideally I'd like to get back to the weight I was at [pre-pregnancy], which was probably around 115."
To that end, she's signed up for the NutriSystem food-delivery program (which she likes because "It's not like you have to go and sit through a boring meeting," she tells ET
) and has been spotted jogging with husband Dean McDermott
But being concerned about her weight is new to her, she says. "I've been lucky. I don't know if it was genetics or age. I would eat healthy at times and pig out at times, but I never had to go on a strict diet plan."
While she was pregnant, she had mixed feelings about her changing body. "I went back and forth," she says. "I would have some days where I would feel really proud of my tummy and walk in front of a mirror and be amazed by it ... and I'd have some days where I felt like a whale. I gained weight in places that I didn't know I could ever gain weight in."
Still, her weight worries haven't dampened her joy at being a new mom. "I'm on cloud nine 24 hours a day," she says.