Why my dog is sleeping so much?

Hello everyone, I have 1 dog of 25 days when I bring him yesterday. But from yesterday I observed that he is a lazy kind of pet and he waste most of the time sleeping. I don’t know this is right or wrong. And whenever I am going towards him he acts like he is an energetic pet but it is not like that. I wish that some specialist who has knowledge about this topic will help me get out of this situation. I want to make him healthier so please guys help me and even provide me some tips to give him a healthy diet. And what should I include in his diet plan?

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