and lump below stitch site indicates a collection of blood caused due to injury.This local collection of blood is called as hematoma
and it generally resolves of its own gradually.However if it becomes infected,then it will cause local redness
,intense local pain and sometimes fever.
In that case it would require drainage
and a course of antibiotics.
At the moment,there is nothing specific is to be done and take usual antibiotics and anti inflammatories,which must have been prescribed to you by your doctor.