Not enough milk?

I feel like my 3 week old is starting to not get enough milk 😟 today he’s been extra fussy and will nurse for 30 minutes. I alternate boobs each time, but it seems as if my right boob doesn’t have as much milk as the left. Even when I pump the right boob only gets 20 ml while the left can get up to 2 oz. I put him on the right and he was eating for 20 minutes, he stopped and then started screaming like if he was still starving so I put him on the left boob. Idk if I’m making sense lol I’m sorry. I’m just worried he’s not getting enough ☹️