Strong restless desire (4)
(Other definitions for itch that I've seen before include "Restless longing" , "following seven years in union?" , "Nagging wish" , "burn" , "Tingle" .)
'strong restless desire' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for urge that I've seen before include "Plead" , "Constrain" , "Advise strongly to press forward" , "Press to take action" , "Persuade - proclivity" .)