Milk supply is almost gone :(

So i got cholecystectomy 3 days ago. It was a complicated case as the stones had moved towards the liver. I had to take medication that weren’t breastfeeding friendly. So I stopped breastfeeding on thrursday night. I didn’t pump but hand expressed whenever it hurt too much. I had a good supply of milk before. My baby was happy and growing healthy. Underwent surgery on Monday (3 days since I stopped breastfeeding) came back home on Tuesday. And tried feeding my baby on Wednesday. Now there’s little or no milk. I was in such pain before surgery I couldn’t wrap my head around anything. Now I’ve ordered a breast pump. I’ve heard of power pumping. Can anyone help me out? How do I bring up my milk supply? My baby is 7 weeks old