Article to say rather too much about one’s pain (7)
I believe the answer is:
anguish
'pain' is the definition.
(anguish is pain or suffering)
'article to say rather too much about one's' is the wordplay.
'article' becomes 'an' (indefinite article).
'to say rather too much' becomes 'gush' (gush can mean to talk about something too much).
'about' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'gush' placed around 'i' is 'guish'.
'an'+'guish'='ANGUISH'
(Other definitions for anguish that I've seen before include "Severe pain, may be mental" , "Severe pain, physical or mental" , "Great suffering" , "Mental torment" , "Severe mental suffering" .)