I can't tell from your response completely... you're getting 1 oz or less if DS is NOT nursing on the other side... but more if he's nursing while you pump?
My guess is that you are not having a letdown for the pump. I had this happen to me from time to time, and it happens more often if I am tense. I'll get about an ounce of drip milk but nothing else happens. But there's plenty of milk there, and later I'll find I'm engorged - the milk just didn't come out with the pump.
For me the trick was just to R-E-L-A-X a bit more while pumping. It's harder to do when you don't have a sweet baby in your arms to melt you. I read very light reading material - People Magazine is a good one

Just some trash to keep your mind off the day's events so you can unwind enough to have a letdown. Try whatever works for you - soft music, journaling, sending e-mail...
I also found that it was very difficult to let down if i was only pumping one side, but I was pretty successful if I double-pumped. If you're not using a double pump, try renting one for a few days and see how it treats you. You will need to buy the pump accessories. If you're planning to work 3 days a week for quite some time, it'd be worth investing in a Pump in Style or Ameda Purely Yours (I think the PY is cheaper and I've heard it's just as effective).
Good luck!