There are several medical issues that can interfere with potty training. Dogs with a urinary tract infection (UTI) will urinate frequently in small amounts, and will not have much control. You may also notice excessive licking of their genital region. If you notice a change in the consistency of their stool, the cause could be a gastrointestinal issue. Some common causes in puppies are intestinal parasites, having eaten something not in their normal diet, or a sudden food change. If a food change is necessary, do it gradually over 5 to 7 days. If you suspect any of these issues could be a problem, you should consult with your veterinarian.
Remember that training is an ongoing process. You will never be completely finished. It is important to keep working on obedience training throughout the life of your dog. People who learn a language at a young age but stop speaking that language may forget much of it as they grow older. The same goes for your dog: use it or lose it. Running through even the most basic tricks and commands will help them stay fresh in your dog's mind. Plus, it's a great way to spend time with your dog.