5 month does no longer sleep his hours

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Okay so my 5 month old does sleep in the night any more. Well he's bed time is at 9 and he would just wake up to get feed now he's stays awake for a while before going back to bed again. Why is he suddenly doing this. How can it fix it. I don't know what to do anymore my husband and I were use to his old sleep schedule not this one please help