Lookalike agrees regulars are pains (7)
I believe the answer is:
twinges
'are pains' is the definition.
(I have seen 'Sudden pains ' mean 'twinges' so perhaps 'pains' could also mean 'twinges')
'lookalike agrees regulars' is the wordplay.
'lookalike' becomes 'twin' (twin can mean a lookalike).
'regulars' means one should take alternating letters (letters selected at regular intervals).
The alternating letters of 'agrees' are 'ges'.
'twin'+'ges'='TWINGES'
(Other definitions for twinges that I've seen before include "Small stabs of pain" , "having some discomfort" , "Sudden pains" , "Sharp stabs of pain" , "Small or mild darts of pain" .)