The 26-year-old and husband Austin Green, 39, welcomed baby boy Noah on September 27 after keeping a relatively low profile during her pregnancy, reported Us magazine.
"The whole thing has been overwhelming because I didn't realize you could love something so much, and I know people always say that but I love him so much it hurts.
And it's an interesting feeling to have because I never felt that before.
"He's getting to that place where he's smiling and he's almost ready to laugh, and I can't wait for that baby laugh that almost makes you feel like you can fly, like your heart's going to explode," she said.
Noah's name is a Biblical reference, Fox explained.
"I went through a stage in my early 20s when I was very rebellious against how I was raised and I wasn't worried about faith or religion but now, maybe because of getting married and wanting to have a family, I've come back full circle."