Night time help

My newborn will be 3 weeks Friday and I’m having nighttime issues. She will go 2-4 hours where she has been fed and has a clean diaper and won’t sleep. She doesn’t cry but will move her head back and forth on my chest like she is hungry, but only suckles a few times. I’m not sure what to do, especially since she doesn’t cry, sometimes she is a little fussy. I’m lost on how to help her.