Should I Be Worried About Viral Endocarditis In 7 Year Old?

Hi,my son is nearly 7.He has had flu like symptoms for a week now.Fluctuating temperature,increasing productive cough with infective sputum,had a unilateral tender shoulder (R) which came on spontaneously at the same time but resolved mid week.He has remained doing about half of his mormal activities during this time but is still more lethargic than normal and decreased appetite.He maybe just recovering from a chest infection but his spiking temperature remains particularly starting at mid day and at night.I am a physiotherapist and have attempted to listen to heart sounds and ? whether there is a S3 present over the Mitral valve area.There is a familial history of heart problems in the family and therefore am just wondering whether I should be concerned about viral endocarditis at this stage?