Why is my baby girl now asking for milk less often than before?

Bianca
In her first month, she almost always drinks every two hours or less, but now she can stand 3-4 hours (esp at night) without drinking at all.
She's exclusively breastfed, and currently 2 mo.
Is that normal? What's your experience?
How to tell if she's getting enough milk and feeling full? She also sleeps less and becomes more sensitive to noises and easily wakes up.