Need some help

Things were going fine breast feeding and by week 2 i felt like my baby and I finally were in a rhythm. Then my baby needed surgery where he couldn't eat food for 2 days, I pumped in the hospital but after 5 days of not being able to breast feed my milk feels like it's gone... I have tried pumping and feeding every hour but nothing has seemed to work to get my milk back and I feel like my baby is starving. He already lost a pound from the week in the hospital so I can't afford to have him not eating. Anyone know if I lost my milk for good or if I can work to get it back & any tips ? I'm a FTM and my baby is now 4.5 weeks old... Thanks!