The former Sugarland star also got candid about the transition into motherhood, thanking fans for their support and explaining that "the rhythm of my life is way different than the movement and pace before baby. In short, this baby is the boss of me."
She went on to say that Magnus (whose daddy is Nettles' husband, Justin Miller) began his "boss" career from inside the womb, where he stayed four weeks longer than he was supposed to.
Once he arrived, Nettles says she discovered that being a mom means learning new things about herself -- including just how painful it is not to get enough sleep.
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"There is a reason why sleep deprivation is one of the first stages of torture: You'll tell someone anything and they won't even have to touch you," she jokes. "'Mommy brain' is absolutely real as a result of your brain being deprived the sleep it needs to function normally. I was making a grocery list and said to my mom, "What's it called? A 'glass' of peanut butter?" She said kindly, 'No honey, it's a JAR!' Dear Lord! And so I am reveling in and hopefully gracefully fumbling through, this most beautiful, challenging, precious, sleep deprived time as a new mommy."
Nettles, 38, also shared the photo on Twitter, along with a holiday message: "So much love and joy on my first Mother's Day! A very Happy Mother's Day to all the Mamas!"