Hi, here are some general information on babies' sleeping pattern which you may find useful:
https://www.sgh.com.sg/Patient-Services/conditionsandtreatment/Pages/Sleep-Advice-Parents-Newborns-Infants.aspx
It is noted in the article that most babies between 3 to 6 months old do not sleep through the night. Usually, a baby would gradually increase the amount of time they sleep at night as they grow.
The article also highlighted some tips to help babies learn to sleep longer at night.
Another article that may be useful is this, which discussed different sleep training methods. You can have look and see which method you are comfortable with:
http://www.newagepregnancy.com/sleep-training-baby/
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