Do you have a hands-free pumping bra? That helps, because you can massage your breasts while you pump. You should get more milk out that way.
In the mornings, you tend to have more milk... so that is probably why the after-feeding session produces the same amount as during the work day.
I had to pump religiously every 2 hours (for a half hour each) in order to get enough milk for the next day. That meant 4 times at work, and one time on the drive home. As I got closer to DS's 1 year birthday, I was having to also pump once more before I went to bed. It took a lot of energy, but it was definitely worth it!
Try not to focus on how much you get at each pump session. If you get 2 oz at 10am, you might make up for it at 12pm or 2pm. Relax while you are pumping. You can do it!
Mommy to Alex, born 2/27/11