"I have this thing, like one percent of women get, it's called hyperemesis," Kelly reveals to the radio show.
Hyperemesis gravidarum is a pregnancy complication characterized by severe nausea, vomiting and weight loss.
"It's horrible," Kelly says bluntly. "It's like the darkest places I've ever been in my life."
"I'm familiar with all day sickness," she also told CBS This Morninglast month. "It's pretty bad. I have to get IVs and fluids, I get so dehydrated. It's really bad."
Still, the original American Idol champ obviously couldn't be more overjoyed that she's expecting again with her hubby. Kelly adorably announced she was pregnant with her second child during her concert at the Staples Center in Los Angeles in August.
"I was not planning on announcing this. I'm totally pregnant again," Kelly said, laughing. "That was not planned. I just didn't want you to think I was crazy. Honestly, I'm just hormonal today. Nothing's wrong. I'm OK. I haven't vomited yet!"
In October, Kelly announced she was expecting a baby boy on Instagram. "In other news, River's gonna have a little baby brother :) #itsaboy We're so excited!" she wrote alongside an adorable picture of River on a slide.