First - did you get him from a reputable breeder? Some puppy mills are disguised as legitimate breeders. That would explain a lot of how your puppy is behaving.
Aside from that, you've only had him a few days. He will need time to adjust. Weeks for sure. Let him explore and come around on his own time. Don't even worry about taking him for walks right now. Let him settle in to his new life first. He's just gone through a huge change! After a couple of weeks start taking him out for just short walks, stay close to home. Eventually you can take him out longer and longer.
Basically just go slow and let him settle in and adjust to his new life.
Aside from that, you've only had him a few days. He will need time to adjust. Weeks for sure. Let him explore and come around on his own time. Don't even worry about taking him for walks right now. Let him settle in to his new life first. He's just gone through a huge change! After a couple of weeks start taking him out for just short walks, stay close to home. Eventually you can take him out longer and longer.
Basically just go slow and let him settle in and adjust to his new life.