Big Hugs, Brianne! I know how you feel, as my milk supply dwindled with Luke as well right around 4 months when I returned to work. I had to quit pumping, but he stayed fairly healthy irregardless of being formula fed! 10 oz is still a great contribution to her daily diet!!!
This time around, I have an enormous supply with Levi, but I attribute that to pumping like a maniac from Day 1. I was not able to start straight away with Luke, as I was sick myself. Have you tried pumping shorter sessions, and more frequently? I do believe that it's required by law for employers to allow breastfeeding Moms time to pump. I know I've really had to work with my employer on this. Do you use a hospital grade pump (I have a Medela Pump N Style Advanced and love it!)? Is your fluid intake sufficient? I'm sure you've probably already tried these things, but just thought I'd offer what has helped with me!
And Congrats on little Kyndall's weight! Levi is only 3 days older than she, and altho I'm not real sure on his current weight, he was only 8lbs 13.5oz at his 2 month check-up. I'm sure he's not 12lbs :) My boys just don't seem to "tank up". What's your secret?! :)