I put on pounds when out of sorts (3)
I believe the answer is:
ill
'out of sorts' is the definition.
(I've seen this before)
'i put on pounds' is the wordplay.
'put on' is a charade indicator (letters next to each other).
'pounds' becomes 'LL' (two L's - the pound symbol is based on L).
'i'+'ll'='ILL'
'when' is the link.
(Other definitions for ill that I've seen before include "Shakespeare: '. . . met by moonlight'" , "Where to find Chicago" , "Misfortune" , "Not in the pink" , "US state" .)