Looking for advice on milk supply!! When I first started to pump (he didn't take to the breast) 😢, I…

Looking for advice on milk supply!! When I first started to pump (he didn't take to the breast) 😢, I was able to pump 6 oz or sometimes more from each boob!!! I'd end up with 12-14 oz of milk a pumping.... And I pump between every 2-4 hours. Now I do good to get 2-4 oz pumped. My baby is 3 weeks old and eats 5 oz of milk about every 4-5 hrs... My supply keeps going down and idk how to get it back up! I don't wanna loose it bc I really want him to have breast milk. Any ideas as to how to get my supply back up?!?