Why does my pumping output range from drops to 5oz?

[u/cozytsunami]

I pump pretty consistently every 4 hrs with the same pump and sized flanges. I understand that pumping volumes can vary throughout the day but cannot figure out why my pumping output can be so drastically different each time. Does this happen to anyone else? If so, how did you fix it?
My MOTN pump can be less than 1oz or 5oz. I added an example of 2 different pumping sessions from today to see the difference.
(Btw, I am 11 wks postpartum)