Establishing a milk supply after several weeks

Averi
Hi ladies,
Does anyone know if it is possible to establish a milk supply 4 weeks after giving birth?
I attempted pumping while in the hospital, and it was almost like the milk never came in, and I was producing very, very little.  I feel terrible and am beating myself up for giving up on it too easily.  I did a little searching and found that sometimes it is possible to establish a milk supply several weeks after birth.  Does anyone have any experience with this, or been through something similar?  Thanks in advance!