I have very difficulty to produce breast milk. I produce only 4 oz a day. Almost give up, can anyone give me advice on how to increase quantity?

Some people take milk boosters to help to increase their supply. However this takes times because different foods work for different people so you need to do trial and error to see what works for you. The fastest and most effective method for me was to do power pumping. So you pump for 20 minutes, rest for 10, pump another 10 and rest for 10 and the last pump at 10 minutes. Takes about an hour but I see increased milk flow for the next 24 hours and the effect is maintained. You can do it once everyday till you are satisfied with your supply.