Milk production low??u

Hello my baby iscurrently 3 weeks old i am partially breast feeding ( pumping ) there for 5he first week or so i had a hard time trying to stay on top of pumping every 2 hours, butnow i been trying to pump everytime my baby eats and it seemed like all was well at first i would get at least 1 oz from each Breast but today im struggling more with only getting maybe 1/2oz from each breast. I currently use a manual pump and pump for at least15 min each total 30 min, and i only express milk in the first few minutes anymore it used to be a good oz in 5 min the other 10 min was just to increase my supply. Could this mean im losing my supply???