When you express your milk, do you notice how long will your letdown come in? Some people takes longer for the letdown reflex to kick in and baby starts to get impatient. One way to overcome this that I've read is to pump a bit first to stimulate the breasts before letting baby latch so that baby will get to the milk faster.
When you latch your baby, is your baby properly latch? How long do you latch her on for each breast? Do you breasts feel softer after she latches compared to before she feeds? If your breasts dont't feel softer, chances are, she's not emptying your breasts properly. For different positions for latching baby, you can go to this website below:
How do I hold thee? Positions and tips for making breastfeeding work | BabyCenter
The reason why people say milk flow will be established from 6 weeks on because the demand for milk would have already been established which causes the body to produce that amount of milk. During growth spurts, it is also important to latch your baby than supplementing with FM so that your body will get the signal of increased demand.
The only way to increase supply is to latch your baby. There are mummies here who drink tea and eat pills to increase supply too. You might want to check those threads out.
Pumping 100ml is actually not too bad. I was also pumping about the same amount when my baby was your baby's age.