My 8 year old had strep at lwast 10 times last year. he had a recent strep test that was negative but he has had a fever for over a week now could he have rheumatic fever?

Not necessarily : It's true that rheumaeva fever patients have fever. They also have other manifestations such as rash, joint swelling, cardiac involvement etc. But be certain that that is the true cause of his fever because it could be something else. Your physician will be the best judge of what's going on. He needs to be seen.

Rheumatic fever: Rheumatic fever usually follows a strep throat about 2 weeks after the diagnosis. Since the strep test was negative, his illness looks more viral in nature. If the fever persists and your son is feeling tired, achy and has swollen glands loss of appetite, bring him back to the doctor for blood work to rule out mononucleosis.