The lump that you are seeing after surgery could be Seroma
Because of mesh and dissection done during procedure,some collection might be present beneath the umbilicus
Go for an ultrasound
abdomen to know the nature of the swelling.If it contains clear serous fluid,then nothing to worry.If pus is collected,then it should be drained.
It is better to consult your surgeon if you develop fever
and pain locally.
Wish you speedy recovery