Ok, so first -- way to go for being so dedicated to your daughter and her health! You can keep doing this, don't let anyone discourage you!
Ah, yes, the pump. It's a love-hate relationship, isn't it?
FYI: I very very recently moved cities and now work from home most of the time, so I'm not pumping on a daily basis anymore. That's why most everything I'm about to say is past tense :-)
I went back to work after my daughter was born (now 9 months) and I found pumping to be a challenge. At first, I got so much milk. After a few months, my supply seemed to be dwindling. I got some great advice from some already mentioned sites (workandpump, kellymom), and some from friends as well.
Stress can definitely be a factor. A big factor. And the more you stress, the less milk you'll pump, and then the more you'll stress... it's a losing cyclical battle.
Liquids is also a big one. And eating enough! I also found that pumping consistently at the same time each day helped my production at the pump. And you're possibly undergoing hormonal changes now? Has your cycle come back yet? I think that can affect how much milk you're producing/pumping. I believe it may dip and recover based on your hormone levels once your cycle returns.
And another big one -- responding to the pump. At one point I wasn't pumping much milk. But I actually had plenty of milk! I would have FULL breasts, and just not be able to pump much. It was so frustrating! I could hand-express and get milk, and then I'd stop, and get nothing (or very little) from the pump by itself. And then my body started making less milk b/c it thought I didn't need it anymore during the day. Ach lamon! Some women (like me) do stop responding after awhile, and you have to figure out how to "trick" your body into making milk for the pump again or getting the milk out with the pump! This may be your problem, not your supply.
If that is the case, maybe try a different pump (I hear manuals can sometimes get a LOT of milk when a double-electric starts to fail since you can control the stimulation, similar to hand-expressing). I also started massaging while pumping. I would use my hands-free to hold the pump/bottles in place, and then use my hands to firmly stroke along the ducts down towards the bottles. I usually got more milk this way!
Oh, and I had to stop watching the bottles fill (or not fill!). I also did extra pumping sessions at night in order to get more milk if I needed it.
If it IS your supply, I second all the advice about the tea. If you don't like licorice, you can get tea from here that doesn't have it in it:
http://www.bulkherbstore.com/Mamas-Milk-Tea
That is actually the tea I used. It was great b/c it's cheaper in bulk, and I drank a LOT of it. I would make a pitcher and leave it in the fridge. I also bought tea-sacs and used them to make individual teabags for work, and then I drank a couple cups of hot tea a day at work.
There are other places you can get tea as well (which have already been mentioned). One that hasn't been mentioned yet is the milkmaid tea from earth mama angel baby:
http://www.earthmamaangelbaby.com/milkmaid_tea.html
And, there are other supplements as well. Motherlove makes some:
http://www.motherlove.com/products_extracts.php
Some of those are so strong they're supposed to be able to help non-lactating people (such as adopting mothers) lactate! I think you can buy them at Whole Foods. I can get them at a local health store in my city as well.
Also, in order to make sure I kept my supply up, I let her have unrestricted access when I was at home (granted, she was younger than your babe and you said you took out a session already. You have to judge for yourself whether that fits in with your overall plans). I also co-sleep so she eats often during the night (also might not be something you're interested in), which definitely helped keep up my supply.
Regardless, I found that making sure I had LOTS of capacity for milk (along with helping the pump with stimulation) was the key for me. That way, I gave the pump the best chance at getting enough milk. I never had trouble with too much milk (clogged ducts or anything), doing that. YMMV.
Try one idea, try them all -- I'd love to help more if I can. Best of luck!!!!