This could be an abscess (infection or pus in general terms). Get it check ed immediately. It could be tooth infection or gum infection. If there is no pain or swelling, it is all the more important that you get it checked by a dentist at the earliest. This is because the silent ones cause more damage. In simpler terms, if there are no symptoms, damage is occurring and it is not presenting itself. By the time it presents itself, damage done will be extensive and beyond repair.