K.S.
My son and my sister's son both went through the same thing. Mine had been a terrible sleeper at the beginning and only really slept through the night from month five to month nine but my sister's son had always been a good sleeper and suddenly at nine months stopped sleeping through the night. Maybe it is a developmental milestone they reach at about that age that has some impact. Or maybe they are just growing like crazy and it makes them restless and starving. Who knows? But we both experienced this as well.