Hi~4 months old might still have night feeds so dun worry. Reduce of intake might be due to environmental such as different rooms or places or even different people feeding him, insecure might be a factor. Some babies are more sensitive to changes. Any reduction to scoops of milk powder? Some babies can pick up difference in taste of milk. Need to think about all possibilities.
U can consider not to let baby nap too much in the day so that he might be able to sleep better at night. Their sleep pattern will change from time to time esp he is still young. By 6 month baby should be able to sleep through the night. I hope its helpful.
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