Anger follows a month of fever (7)
I believe the answer is:
febrile
'of fever' is the definition.
(I know this)
'anger follows a month' is the wordplay.
'anger' becomes 'rile' (rile can mean to annoy or anger).
'follows' is a charade indicator (letters next to each other).
'a month' becomes 'Feb' (abbreviation for February).
'rile' put after 'feb' is 'FEBRILE'.
(Other definitions for febrile that I've seen before include "Of or involving a fever, feverish" , "Overheated" , "Delirious" , "Very hot" , "Showing nervous excitement" .)