Thanks for the responses, ladies. I called the doctor with some follow up questions, and another doctor in the practice told me to try Alimentum because he doesn't think that Gerber Good Start is different enough from Similac. I ended up trying Alimentum with her and she HATES the taste. I'm just at a loss.
The doctors and nurses in the practice all seem to have different opinions, which I understand since it's hard to decipher what's going on with a little baby.
We're going to try sticking with Gerber for now, and if I need to try something else, like Similac Sensitive, then we'll try that. I'm seeing from your stories and from other research, that it is a guessing game and we have to find what is right for us.
Maybe I'll figure this girl out by the time she's in college!