Can’t produce a lot of milk

I started breast feeding about day 4 of my babies life, I told DR I was doing both but the never gave me a pump to pump while I was in hospital so I had to wait until my breast pump came to my house after I got discharge. Well he’s now a month and I’m still only producing about 4oz BOTH BREAST TOGETHER ,he’s on 6oz . The only time I can produce 5oz or more is when I go a long period of time not pumping. But if I do the every 3 hour pump then I get only 4oz with both breast together . I already tried the mother’s milk tea, seem to not work. I drink lots of water . Nothing works