Kim Kardashian -- Obsessed with Breastfeeding Baby North West

Kim Kardashian's breasts have swelled to a record-sized G-CUP following her pregnancy -- and sources close to the reality star tell TMZ, she LOVES whipping out her massive new mammaries for baby-suckling time.

Sources tell us, Kim's taking to motherhood like a newborn to a nipple -- in fact, she actively looks forward to her "feedings" with baby North West ... EVEN CHANGING DIRTY DIAPERS!!! As one source put it, "She does it all."

It's pretty crazy ... considering how vocal Kim's been about motherly duties in the past. Back in 2010, she got into hot water for criticizing a mom for breastfeeding at a restaurant.

EWW Im at lunch,the woman at the table next 2 me is breast feeding her baby w no coverup then puts baby on the table and changes her diaper

— Kim Kardashian (@KimKardashian) June 19, 2010

As for Kanye, we're told he's a natural dad -- "No one has ever seen him like this."

Now for another famous G-cup ...