Allison F below has some good advice. It seems obvious that you make plenty of milk (baby is gaining weight and isn't fussy). So I don't think that you need to make more milk, but rather that your body doesn't respond to the pump easily - this is common, but can be hard to address. With that in mind, a few other thoughts:
How long are you pumping for? When I pump, I get an intitial let-down, and then the flow slows and stops. But if I keep pumping a little longer (between 15 and 20 minutes from when I started) I will get a second let-down that is almost as much milk as the 1st (so going from 2-3 ounces total, to about 5 ounces total). So to get the maximum amount of pumped milk, I need to pump for 30 minutes.
Allison mentioned during the pump down low to get a second letdown. Other moms I've talked to recommend actually stopping the pump for 5 minutes after the initial letdown of milk stops, and restarting the pump to get the 2nd letdown.
This is a personal thing but - some people get more milk if they sit quietly, look at a picture of their baby or even close their eyes and imagine that they are nursing. Some people get more milk if they take their mind off of the pumping completely and read the newspaper or watch TV. However, most women I know get the least amount of milk if they sit watching the pump, feeling stressed that not enough is coming out. So try to do something that relaxes you while you pump.
Also, don't go too high with the pump. I actually get more milk when my pump strength is a little lower. If it starts to feel uncomfortable to me, then the amount of milk I get drops (maybe because I tense up a little or something?).
I also wonder if you are over-estimating how much milk you need to pump for your baby (see http://www.kellymom.com/bf/pumping/milkcalc.html). Sometimes babies will finish a bottle simply because it's there, even after they are full. If you gave her a 5 ounce bottle instead of 6-8, would she fuss when it was empty? You might be surprised to find out that she's just as satisfied after 5 oz as she is after 7 oz.
You don't say how your your baby is, but if she's old enough maybe she would be interested in some oatmeal cereal or something similar, instead of one of the bottle feedings when you are not around. That would decrease the amount that you need to pump when you are away from her.
Good luck