Credit: Jason LaVeris/FilmMagic

Kourtney Kardashian is chomping at the bit to give birth to her baby boy -- and to get thin again.

After the eight-months pregnant star admitted last week that she is "over the red carpet being pregnant" and has gained 26 pounds, sister Kim admits that Kourtney is "having a hard time" accepting the added pounds of pregnancy.

"Kourtney is going crazy," Kim told at the opening of Westfield Culver City shopping center in Culver City, Calif. Saturday. "She feels so big right now. She's just ready to have the baby."

Kourtney's son with boyfriend Scott Disick is due sometime in December.

"I think once you get to that final month," Kim said, "you are just so anxious to have the baby."

At the moment, Kim and sister Khloe are both dieting with the QuickTrim product -- and their with-child sister is jealous. "She is anxious to get on the same plan as us," Kim, 28 said. "She sees a definite difference in weight loss from us. I feel like I am in the best shape of my life right now."

As for Khloe, the newlywed Kardashian still has a ways to go: Thursday she revealed that she's gained five pounds since her wedding. "I stopped my QuickTrim diet for a little bit around the time I met Lamar [Odom]," she admitted. "I was so in love, and I was at my perfect weight, and I didn't want to do it anymore."