The country star, known for tracks including "Jesus, Take the Wheel" and "Before he Cheats", said it was the first moment when she was honest with God about her feelings.
Underwood, who has a three-year-old son with her husband, told CBS News' broadcaster Tracy Smith: "I had always been afraid to be angry. Because we are so blessed.
"And, my son, Isaiah, is the sweetest thing. And, he's the best thing in the world.
"And I'm like, 'If we can never have any other kids, that's okay, because he's amazing.' And I have this amazing life. Like, really, what can I complain about? I can't.
"I have an incredible husband, incredible friends, an incredible job, an incredible kid. Can I be mad? No."
Underwood married her husband, NHL hockey player Mike Fisher in 2010, six years after she swept to victory in the American Idol talent contest.
Since then, the 35-year-old has sold 64 million records and been awarded seven Grammy awards.
Explaining how she wrestled with questions about her miscarriages, Carrie said: "In the beginning it was like, 'Okay, God, we know this is, just wasn't Your timing. And that is all right. We will bounce back and figure our way through it.'
"And got pregnant again in the spring [2017], and it didn't work out.
"Got pregnant again, early 2018. Didn't work out. So, at that point, it was just kind of like, 'Okay, like, what's the deal? What is all of this?'"
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