From my experience, when an older baby pulls off and on the breast,
he/she is just curious about what's happening. This is very typical
starting 4 months. But when a young infant isn't settled and keeps
arching back, it could mean an over-active let-down. The milk is coming
down so fast, the baby has a hard time keeping up. I would advise
expressing a little milk till the flow lessens.
Susan Nachman-Srebrnik, IBCLC
Ranana, Israel