The reality star and mom-of-four lifted the lid on her pregnancy journey while answering fan questions on her Instagram story ... empathizing with a woman who says she's had six failed IVF attempts and asked Kourt how she kept pushing through the struggle.

Kourtney gives her numbers in response ... saying she gave up after a year in which she did five IVF rounds and three egg retrievals -- believing the whole endeavor hopeless.

KK says she relaxed, believed in God's plan ... and, she finally did happen to get pregnant. She ultimately recommends prayer and belief to the fan struggling.

Kourtney, obviously, had three other kids before welcoming Rocky to the fam ... so, it's a pretty intensive regiment to go through for a non-first-time parent -- highlighting just how determined Kourt was to have a baby.

Kourtney and husband Travis Barker's son, was born last November ... and, Kourt's been very honest about the trials and tribulations of motherhood in recent months.

Remember ... earlier this month Kourtney relayed her postpartum troubles at work -- and, she also shared her terror at Rocky having fetal surgery on an episode of "The Kardashians" last week.