In an interview with BBC Radio, the “Stronger” singer said her nausea was so bad that she would throw up up to 25 times a day.
"I had to kind of take longer off because I had such a horrible pregnancy – like, I was like hospitalized,” she said. “It was just a bad pregnancy so I had to take off way more time than normal.”
Clarkson, 32, gave birth to daughter River Rose seven months ago.
ABC News’ Dr. Jennifer Ashton said such extreme nausea was “consistent with a diagnosis of hyperemesis or HG.”
Ashton, a practicing OB/GYN and senior medical contributor for ABC News, said hyperemesis can be very serious.
"We don't know what causes it but we do know how to treat it and that could be anything from changing their diet, to needing to hospitalize them to placing an indwelling feeding tube in some cases,” she said.
Despite the challenges leading to River’s arrival, Clarkson said motherhood has changed her for the better.
“You have a baby and you realize how much of a complete crap you were. ... I've never been, like, horrible -- I just mean, I guess, just, in our job in the entertainment world we get very self-involved and, like, everything is about you so, it's nice to have a different perspective,” she said.
Clarkson, who is married to Brandon Blackstock, said she already wants another child.
"I love it. I love it,” she said, speaking of being a mother. “(River)’s pretty awesome and my husband is running from me because I want another one.”
Clarkson’s new single, "Heartbeat Song," was released on Monday.