[Not again!] (4)
(Other definitions for sigh that I've seen before include "Exhale loudly" , "Sad exhalation" , "Exhale deeply" , "Vocal expression of weariness" , "Melancholy moan" .)
'not again' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ugh that I've seen before include "Exclamation of disgust (3)" , "Exclamation of horror" , "Exclamation of disgust, at 22 ac say" , "It's nasty" , "How repulsive!" .)