First of all, 7 weeks is too young for a puppy to leave it's mother. That said, your puppy is just that - a baby. He is missing his mother and his litter mates. He is used to their warmth when he sleeps, as well as the smell of them, and the rhythm of his mother's heartbeat.
Put a shirt or towel that has your scent on it in his cage with him. Put a warm (not hot) water bottle under his bedding to keep him warm. You can also put a clock that ticks next to his cage to simulate his mom's heartbeat. Put the cage in your room so he knows you are near. Soon he will calm down. You've only had him for one day! Give him a chance to get acclimated. He is scared and nervous, as you would be if you were suddenly taken from your family!