If you have had your belly button piercing recently, the pain and pus is due to infection. You will require a good antibiotic cream locally and oral antibiotics and painkillers. Also, you can take a Tetanus Toxoid injection. If your belly button piercing has been done some time ago, remember that jewelry, especially artificial, contains many contaminants such as nickel, copper, chrome, etc. which can cause allergic reactions and inflammation. If this is the case, change the material of the belly button jewelry. After belly button piercing, the care and hygiene demands of this area increase. Avoid wearing tight clothing and belts over this area.