Could Lump On The Collar Bone Of Child Be Harmful?

my son is 7 years old and healthy. during the last 2 weeks of dec he was sick with upper respiratory virus and severe ear infection. yesterday I noticed a small, rock hard, pea size lump that is fixed right on his collar bone where it meets the sternum. I know everything about this points to something serious but is there a chance it is not something serious? im very worried and dont see the doctor for 2 days.