Most of the babies have sleeping problem at the starting. I too had a new born baby at my home, my sister's son. He is 6 months old now. But in the starting, when he was 1 or 2 week old, he sleeps whole day but not at the night time and cry alot. Sometime, it is very bothersome but as he was too young too understand all this. He keep crying. We called our family doctor and he said he is on formula milk, which is sometime hard to digest, the baby must have acidity because of formula milk. But this is entirely vary baby to baby how formula milk works to their health. After few months he automatically changes his sleeping routine. If your baby is also on formula milk, this can be the reason.
However, If you are on breastfeeding, make sure you must eat good food which is easily digestible because what are you eating has direct effect on your baby. After feeding your baby, lye him/her down on pillow. This helps babies to digest food.
hope this helps you. Good luck.