As long as she's gaining weight well and having plenty of wet/diry diapers, then she's getting enough milk. That's the *only* way to tell. A pump is not as efficient as baby, so don't ever judge your supply by how much you pump. Also, it's normal for babies to cluster feed in the evenings and seem to not be getting enough to eat. That's how they tank up for a longer sleep at night. Finally, she could be having a growth spurt, and you may feel "empty" for a few days (although you're never truly empty) as she nurses more frequently to build up your supply.
Like others have said, the pill could be affecting your milk supply, and you want to make sure that you're on the "mini pill" to help prevent that. You could also use a different form of birth control for the next few months until your milk supply is well established.
If I were you, I wouldn't worry about pumping to increase your milk supply. Just let your daughter nurse as much as she wants, and she'll increase your supply on her own. You could choose 1-2 times per day to pump just to help build a freezer stash for when you go back to work, but that's up to you. Also, it's normal to only be able to pump about 2 ounces per session (that's both breasts), so don't expect to get 5-6 or more ounces (although you may once you go back to work and aren't nursing all day). www.kellymom.com has lots of nursing and pumping tips that you can try.
As for the spitting, I wouldn't worry too much if she's a "happy spitter." My kids were fairly spitty babies, and we never put them on meds, and they did just fine. Also, lots of spitting can be a sign of oversupply even though you seem to feel otherwise. Oversupply often comes as a surprise to moms, and as she gets older, and your supply adjusts to her needs, the spitting may decrease. We also found that caffeine caused one of my kids to spit more, so there may be a particular food sensitivity that you could eliminate from your diet.
Congrats on your new baby, and good luck!