It's really important to learn a technique that works well for you to let down well at the pump. For me, it was not watching it and being distracted by something else. For some poeple, it's looking at a picture of the baby or something. I used to play tetrus on my phone to distract me. Think "a watched pot never boils".
Additionally, make sure you are pumping long enough. If after 10 minutes, nothing more is coming out, keep going for an additional 2 minutes to tell your body "hey, that's not enough, make more next time". If you have a pump with variable speed and strength, try increasing each just a little bit to see if that helps you to get more.
Also, be confident in your baby's cues. If baby is happy and active, then she's probably just fine. It's a mom thing to worry, and it might not ever go completely away, but be confident in your ability to provide for your baby. Sometimes just changing to a "can do" attitude can make all the difference, and confidence could just be the special ingredient for you and your pump!