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

Congratulations on your newborn! Milk usually kicks in 4th day post partum, so to be able to pump 25ml on your 5th day is great! What you will need to do is continue pumping every 3 hours to stimulate more milk (if you're fully expressing). Otherwise, if you're latching to keep latching on demand. Do remember if you're latching to monitor your LO's wet diaper.

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!!