What blood test can be done to check whether my rheumatic fever has come back that i had when i was a boy?

Big picture: I understand you had rheumatic fever as a youngster and now have pain in three joints. If you have not had a recent strep infection and do not have other symptoms / signs of RF as when you were young, you don't have a recurrence and you need to look for some other cause of your joint pain with your physician's help. Labs are only adjuncts to a good history and physical exam.