It is not usual to have a bulge under your umbilicus
after 4 weeks and that too specially it was not there before your surgery.However since you have no other signs of inflammation,it could just be a wound hematoma
which could resolve in a few weeks.
Your numb pain is mostly related to neuropraxia/paresis
of T10 nerve supplying the umbilical region.This also produces referred pain
to the penis.I would suggest you get a followup with the operating surgeon in this regard.