how do i build up my milk supply

breast feeding has always been a challenge for me.. my daughter is 3 weeks old and after about the first week I had to supplement 2oz of formula a day because after I feed her she cries of hunger.. and now I'm not producing hardly anything.. I've always pumped after I've feed her and in between.. at first I'd get an oz after I fed her and now it's not even a half an oz from both.. and when I would pump in between I would get 2oz total and now it's barely a oz.. every story I've read people are getting 3ozs or more.. what can I do to produce more??.. like I said I pump and breast feed all day long.. I drink at least a gallon of water a day and I'm not eating junk food or drinking any caffeine.. the mothers milk tea didn't help in the past it gave me hives.. I really don't know what to do.. 😔