Thank you for your query.
In case your son also had a bad throat in the past week or two and is now having fever
and pain in his ankles then I suggest that you get him re-examined by a doctor. Following streptococcal throat infection
one can have fleeting pain in the joints which needs to be investigated. The doctor may order some blood investigations to know if it was strep infection and is affecting him.
I hope I have answered your query to your satisfaction.
Wishing your son a speedy recovery.