The actress thought she was tired while expecting her first child, 21-month-old son Oliver Finlay, but this time around she's absolutely exhausted.

The 37-year-old Walk the Line star, who is carrying her second tot with husband and Once Upon a Time co-star Josh Dallas, admits she now feels for other mums-to-be who have to look after a toddler.

"Now I’m running after a toddler, working on a series and doing a press tour (for new animated movie Zootopia)," she tells People magazine. "The first time you feel like you are pregnant for four years. This time, I don't know how many weeks I am. I have to reference my date book!"

Ginnifer, who is actually due this spring (16), also reveals she's developed a craving for watermelon popsicles, rolling her eyes in delight and stating, "They're sweet and refreshing and wonderful".

And her son is doing his best to help mum as she struggles with waves of fatigue: "He definitely understands the concept of a baby,” she explains. "He pulls up my shirt every day and pats my belly and says, ‘Hello baby!’ We kept telling him, 'Your brother can hear you', so he just pushes his face into my belly and talks."

Despite the tiredness and the strain, the mum-to-be admits she loves being a parent.

"My husband and I were talking the other day and saying, 'Remember the days when we would just go to the movies and read a book and just take a nap? All of the free time we took for granted?'" she chuckles. "My husband said, 'And we would give it all up, all over again, for that look on his (son's) face after he has been dunked in the swimming pool and he just comes up out of the water with pure joy on his face'."