Fergie cried in her car when she first went back to the recording studio after giving birth.
The 42-year-old singer has four-year-old son Axl with estranged husband Josh Duhamel, and while she got emotional when she returned to her day job, she hit out at "mummy shamers" who blast mothers for going back to work when they've had a child.
She said: "It's the worst. I remember going to the studio the first couple of times and sobbing in the car. It was the weirdest thing ever. That had never happened to me in my life. I'm going, 'What is this?'
"As a woman ... the men can have all the career in the world and still have children. If you're a mum and you have a career ... it's the mummy shaming, 'You can't do that anymore, you're a mum.'
"What am I supposed to do? I love singing and dancing. It's who I am as a human."
Fergie also admitted she is in a tough situation after she and Josh, 44, announced they had broken up in September after eight years together, but they are remaining amicable for the sake of their son.
Speaking on ITV's 'Lorraine', she added: "It's not easy, it's never easy something like this. But you know, he [Axl] comes first and we've got to make it happen."
Fergie's comments come after Josh praised her as an "amazing mother" to Axl.
He recently said: "She's an amazing girl. She really is. She's an amazing girl and I think more importantly, she's an amazing mother.
"I've honestly sort of kept my head in the sand throughout this whole thing. But, I've heard that there's been, you know, things said about her. She's an amazing mother. That's really what I have to say about her."