I agree with the last paragraph in your post, chill out!!
hee hee
All kidding aside, it is very possible that puppy was super comfy with his doggy mom at the breeders house, and your house is just too "new" for his personality to show through.
If this is any consolation, my pup hated me when I first got him. Ok, maybe hate is a strong word, but he did not want to be around me at all. Over time, he got use to me, and now his true crazy quirky personality shines through. He went from needing 4 ft of space between me and him to him needing to be on top of me.
Do get the puppy checked out for the potential tummy issues. It could be stress, or a true tummy issue that needs to be addressed by the vet. Good luck!!!