I have no expert advice but would like you to know I went through a similar thing a couple weeks ago. My pumping output was totally normal one week and my baby seemed satisfied over the weekend, but when I returned to work on a Monday I was pumping about half of what I normally could pump. My DS was a little over 8 months at the time. I attribute my sudden drop to a couple things: 1. I had a HORRIBLE head cold including an ear infection, 2. due to this I had ZERO appetite and was eating quite a bit less than normal. Also, maybe I just randomly had a slump in supply, I'm not sure.
Slowly it is coming back, and even about 3 weeks later I am not back to my "normal" production. This is what I did: 1. let baby nurse as much as possible. I could tell my supply really was down and it was not just the pump because DS was nursing constantly and a lot overnight too. 2. I went to my local hospital and rented a hospital grade pump. I was also using the Ameda PY pump and I HATED it. Like Mommal says above I also felt it was underpowered, but since my output was always more than baby drank I figured why spend the money for something else. I am still renting the pump from the hospital and will continue to do so until DS is at least a year (only 3 more months).
Keep nursing and pumping (when away from LO) as much as you can. I would def. add in a 3rd session at work. Trust me, I know how inconvenient pumping is at work. I pump three times during an 8 hour shift. I hope some of that helped.