Rooney, 29, said she doesn't know if baby number three is responsible for the changes to her energy levels, or if it is a consequence of having her and Wayne Rooney's two sons, Kai, six, and Klay, two, around.
"I've been more energised, but I don't know whether it's because I have two others to crack on with," she told new! magazine.
"I'm still on the go and running around after them".
Kai and Klay have kept their mum busy this Christmas
Rooney hasn't suffered from morning sickness during any of her three pregnancies, but she has experienced some changes to her skin this time.
"My skin has become a lot drier, so I’m having to moisturise a lot more," she told the Daily Star.
"My gums have also become more sensitive, which never happened with the first two."
Rooney, who is due to give birth in January, managed to spark rumours about whether she was expecting a baby girl earlier this month, however she has said she's waiting until the birth to find out the gender of her third child.
“The first time with Kai, we didn’t find out,” she said. “We did ask the second time with Klay but, with this one, when it came to the crunch at the scan, I had thought I’d want to know – but it turns out I didn’t."