Re: Gas, colic, inbalance??
Phi has given excellent advice and suggestions. I would avoid the pump like the plague, and not block feed just yet. I am not sure how all of this works when there's an older child in the mix- your big kid could be helping to keep your supply on the high side, and I don't know how you'd fix that.
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!"