not producing enough milk

I am so sad and could burst out in tears. my daughter will be 3 weeks Monday and I just switched her to breastmilk yesterday (had to finish mediciation). yesterday she took 3 oz of breast milk one bottle, than the next bottle 2.5 oz breast milk and then it started going downhill. I couldn't pump much. the next bottle 1 oz breast milk than 2 oz formula an than the next bottle 1.5 breast milk and 1 oz formula.... And than i could kill myself, I set an alarm to get up to pump and apparently slept right through it for SIX hours!! yes my 3 week old slept that long !! but I wake up in complete panic and pump 3 oz enough for her to eat. But I am feeling so discouraged and heart broken that I can't pump enough to feed her only breastmilk. I keep telling myself any breastmilk is better than NO breastmilk, but how ture is this? I feel like I can't do the one thing my body is made to do. I've been drinking as much water as I can stomach, eating oatmeal, tried hand expression, tried letting her latch on. tried power pumping too. 😭