CONGRATULATIONS!!!
Like Rose said your body does work on supply vs demand. Feed the baby then pump for 10 min on each side, stay hydrated (drink your 8 8oz glasses of water and what you put out , also put back in on top of that) STAY AWAY FROM SAGE (drys you up) Take Fenugreek pills, or drink the tea. Pump Pump Pump. You body will get it.
But from what I gather is you have the milk there but not at the time he wants it. When are you pumping? You should pump right after he eats, not inbetween, this way you have stock piled for him when he is read.
If he eats at 8am and you pump at 930 then he wants to eat at 1030 you do not have the surplus you would have if you fed him at 8 pumped right after (830 to 840) then waited til he was ready for more then start over.
ALSO Properly Fitted Bra. If you are waring a tight fit that will cause issues too.
Talk/see a lactation consultant, if he is still at the hospital they are there just ask, it is nice to hear you are doing it right keep up the good work.