Re: Weight gain rate low?
I think LLLMeg had some excellent suggestions about assessing the baby's overall health, development, and nursing frequency without looking at the charts. But if you were to assess your baby by the charts alone- which I would not recommend!- it seems like there's no reason to worry. Not based on this chart, anyway: http://kellymom.com/images/growth/growthcharts.gif your baby has dropped some percentiles since 2 months, but as long as she's nursing on demand and with a good frequency, that's pretty normal. Both my kids dropped percentiles between the 2 and 4 month appointments.
Your doc's suggestion to pump after a feeding in order to tell whether or not you are making enough milk is a pretty poor one. It's not an accurate measure of how much you produce, since pump output varies based on time of day, how long it has been since you last pumped, the make/model of pump you are using, and your response to pumping. There are plenty of mamas who can't pump much despite having totally normal milk supplies. I know it's tempting to seek some way to measure your ability to nurse... But in general, there's no need.
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"