She explained new mums need to make keeping themselves healthy a priority and not to hide if they're feeling down.
"I used to announce quite frequently that: 'I'm going to have a cry now' and promptly burst into tears," she said.
"Being emotional is a normal phase that won't last forever."
Willoughby also advised new mums to think of changes to their body as "mummy marks".
"If they weren't there, your little bundle of joy wouldn't be either," she said.
"Your body image mustn't get in the way of your happiness."
Willoughby also covered post-pregnancy symptoms including hair loss and toilet trouble, as well as breastfeeding and confidence issues.