and fever means some infection and not due to medicines you are takink.Intr-articular injections of cortisones are heavy and they are not absorbed in blood and act only locally so no chance for high cortisone level in blood. for systemic effects your blood levels have to be there.
As you mention methtrexate, you must be getting periodical blood check up for count and also LFT (liver function tests)and creatinine
function periodically to see for effects.
500 mg for fever twice and do hot saline (salt)gargles for bad throat.