I would take him to a knowledgeable vet ASAP. With him having come from a pet store, there is a good possiblity of an injury and/or congenital defect. These pet store puppies usually come from horrible conditions in puppymills, then are shipped like chickens to the stores, and then put in little cages and usually are tranquilized til sold. They often have a hard time with housebreaking too because they usually have been taught to live in their own waste. I would get a vet, then find a reputable trainer when the puppy is up to date on shots. And please reconsider ever buying from a pet store in the future. The best place to get a puppy is from a reputable breeder, breed rescue, or shelter. Buying puppies from petstores just puts money in their pockets to keep buying from puppymills, which keeps the puppymills in busineess. Puppies deserve much better than this.
Read through the old threads on here and the educational archive to find out all kinds of advice for the care/training/health of dobermans.
ETA: I'm sorry I meant to say welcome from Tennessee