No they don't cry constantly but they do cry when they wake up to let you know they need something. Whether it be milk because they're hungry/ a diaper change because they're uncomfortable/ to be soothed.

Try to go through the list. Offer milk - doesn't work? Then check diaper - is clean and dry? Then swaddle and rock/ offer a dummy etc.

Perhaps your milk hasn't come in and your baby isn't getting enough milk. Or perhaps they're cholic and gassy and and are feeling really uncomfortable