I'm 5 days post partum, is 25ml for first pump expression considered low supply??

Congratulations!! And 25mk for first pump is actually a lot!! It is only the first pump so usually the amount is not a lot. I think mine for both sides was about 25ml for the first time too. Continue to latch or pump often like every 3hours. Massage your breasts with a warm towel before pumping and the milk will come easier. Good luck!!