Waiting for milk

Jenna • 28 years old been with my bestfriend for 11 years have two amazing outgoing funny boys together an now a girl on the way
Had my baby girl Monday an my breast milk hasn't come in yet. Any suggestions ? She seems so hungry last night an upset with nothing coming out so I gave  in an gave her lil formula even tho I'm 100 percent bout breastfeeding . Didn't want her to starve. Any advice would be great . Been crying thinking I failed an all I want to do is feed my baby myself