Tongue. Brush your tongue. Use mouthwash. See your dentist!
Several things. Bad breath has many causes. Brushing teeth is just one thing to do. Make sure you brush your tongue or use a propriaetary tongue scraper. Use a good oral rinse. Treat any gum or dental problems. Look for tonsillar or adenoidal issues (tip off may be mouth breathing) and get checked for nasal or sinus infections and get treated. If persists, see an ENT or oral surgeon.