Unhappy being in this part of the puzzle? (4)
I believe the answer is:
down
'unhappy' is the definition.
(thesaurus)
'in this part of the puzzle?' is the wordplay.
I cannot quite see how this works, but
'part' could be 'do' (do is a kind of part) and 'do' is found in the answer.
This explanation may well be incorrect...
'being' acts as a link.
(Other definitions for down that I've seen before include "like the other set of clues" , "In a low mood; hill" , "Depressed - drink" , "Fuzz" , "Where this clue is going" .)