The swelling that you are feeling may be a Lymphnode.There will be multiple lymphnodes
in the body,particularly in the Neck region.They will be enlarged in many conditions,but the most commonest cause is Infection.In that case,you may experience pain.
Another possibility is Lipoma
,swelling arising from Fat cells.AS Fat is present through out the body,Lipoma can occur any where.
But,Please consult your Doctor and get it diagnosed by him.If he is not sure,he may order for a simple test called FNAC(Fine Needle Aspiration Cytology).This test will accurately gives the diagnosis.
Nothing to worry.