Kourtney and Kim Kardashian

Kourtney Kardashian is counting down the days until her baby boy arrives — because she can't wait to drop the baby weight.

The Keeping Up with the Kardashians star has gained 26 pounds during her pregnancy, but is "having a hard time" accepting the extra weight, sister Kim tells Us.

"Kourtney is going crazy," Kim Kardashain says. "She feels so big right now. She's just ready to have the baby."

Khloe Kardashian: Kourtney was "miserable" without Scott

Kourtney, 30, who told E! last week she's "over the red carpet being pregnant,"  is also eager to try the QuickTrim diet Kim and Khloe are using. "She is anxious to get on the same plan as us," Kim, 28, says. "She sees a definite difference in weight loss from us. I feel like I am in the best shape of my life right now."

Kourtney's son with beau Scott Disick is due next month.