Does it really happen overnight?

My little newborn is no longer a newborn. I thought I had a few more weeks. I thought I'd see subtle changes, gradually, over time. I woke up this morning and Sophia seemed a little heavier.
Her head no longer had that loose skin wrinkled look. Her cry was throaty and louder--almost demanding, no longer soft and pleading. I changed her diaper and realized her chubby thighs have more rolls and the diaper bites into her fleshy hips. I still have tons of stage 1 diapers, and now I need stage 2?!

I went to put on her onesie that just fit last week and I had a hard time fitting it over her head. I tossed it into her growing pile of clothes that no longer fit. How can it be that overnight, my little baby sprouted into a little girl?