How do I know my baby is eating enough?

How do you know if your baby is eating enough besides weight gain?

He has a wet diaper after every feeding and about 4 dirty diapers a day.

My baby is 3 weeks old and I feel like my supply has decreased over the last 3 days. I tried pumping to see how much was coming out and I only got 1 oz on one side and 2 oz on the other. I kept pumping to try to increase my supply. Since then my nipples are in excruciating pain (too much stimulation?).

Milk used to pour out the sides of his mouth while feeding and now it’s not. He’s also giving me feeding cues constantly.

I really don’t want to supplement. How can I increase my milk besides drinking more water?