One breast barely gives me milk 😭

I've been having a rough time with my production in general. I feel like I just don't have enough for my twins. Right now they are mainly getting formula for preemie babies with the little bit of breast milk I have been getting mixed in. I'm 4 weeks postpartum. In the beginning I feel like it was decent, I was getting about 50 ml from each breast. But now I'm lucky if I get 30. And usually only one breast gives me an ounce, and the other breast gives me about half an ounce. This is what I pumped just now. Does this happen to anyone else?