Are you producing enough milk?
Is she latching on properly?
If not, then she will not be getting enough intake. Hence hunger, even if at breast, and baby will not be satisfied.
That happened, to many of my friends. And it did not get better, until their baby was getting more intake,
3 weeks is a growth-spurt time in an infant.
Infants also do what is called "cluster feeding' in which they need to feed even every single hour. Normal.
Thus, you need to feed on-demand always.
Or does she have an ear infection?
Or gas?
Try Mylicon Infant Gas drops.
My daughter as a baby, had bad gas trouble and pain.
And she acted like your baby.
Breastfeeding, is arduous. But you must feed on-demand. Intake has to keep up with baby. And by feeding on-demand, it also serves to make your body produce enough milk to keep up, with your baby.
My kids as babies, had GINORMOUS appetites and fed often.
Also, is she napping? Newborns typically nap a lot.
ALSO though, babies can act like that when over-tired. AND, they also cry/scream... to Shut-Out external stimuli. If/when tired and/or when over-stimulated.
At this age, even a bath, can over tired them or over-stimulate them.
I would also try, a sleep sack.
If you look on Amazon, they have many.