Anni,
First of all, I'm not a medical professional, and I can't truly tell what might be going on over the internet. Secondly, what you are calling pus may or may not be pus.
Pus is greenish-yellowish in color and is a sign of an infection. If this is the case, you need to go see your body piercer or a doctor for further advice.
Lymph fluids, which tend to be clear to whitish in color, are a natural part of the body piercing healing process. These are produced by the skin and there's going to be plenty of this on and off as your navel heals.