pump settings over time

Hi all! I've been pumping at work for over three months using either a medela symphony or Pisa and have had to use higher and higher levels of suction to fully empty. Massaging while pumping and all that, changed the membranes on all my pump pieces last week and no change. Is this normal to happen over time pumping? Not at the max suction level but it's making me wonder if I'll get there. Thoughts? Thank you all!