re: How to manage fussy Baby?

Babies cry for 2 "reasons". They are hungry or uncomfortable. (some cry when wet or dirty but that ties in with uncomfortable). They cannot be spoiled. If they want to be held, then you hold them. At 3 weeks, the crying you describe is something akin to colic. The baby is hurting. Do your best to fix the feeding issue, whether is not enough or the food is giving her colic. If she needs to be held upright because the colic is hurting her, then you hold her upright. Its not complicated. Go to doc and tell him these issues, he will probably change her to a formula or a mixed formula with breast milk.

PS. you comfort a baby anytime and everytime they cry. Period.