Catherine Tyldesley said an illness left her feeling like she'd "given birth without having a baby".
The former Coronation Street star said she had morning sickness and put on a stone in weight, after her body went through a hormonal imbalance.
Cath, 37, spoke to Hello! magazine about her condition, she said: "My body seemed to think it was pregnant.
"I took so many tests as I was convinced I was actually pregnant and even had morning sickness, but in fact my body was just mimicking a pregnancy.
"My endocrinologist said she'd never seen such a reaction.
"It felt like I'd given birth without having a baby. I put on a stone in weight even though I was eating well and training hard.
"It is only now that I feel I've got my body back."
Cath, who has son Alfie with her husband Tom Pitfield, who she married in 2016, also told the magazine she would like to have another child.
She said : "We are so happy as a three and we don't ever feel like there is anything missing, but would I like another child? Yes, I think I would, so if it happens, then that's wonderful.
"If it doesn't, then I am blessed to have Alfie."
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Cath also said she feels "very passionate" about adoption.
She said: "It is one of the greatest things you can do for another person; there are so many children needing good homes."
*Read the full story in Hello! magazine, out now.