Err so badly, making you more upset (5)
I believe the answer is:
sorer
'more upset' is the definition.
(I've seen this before)
'err so badly' is the wordplay.
'badly' indicates anagramming the letters (letters in the wrong order).
'err'+'so'='errso'
'errso' anagrammed gives 'SORER'.
'making you' acts as a link.
(Other definitions for sorer that I've seen before include "Comparatively vexed" , "more upset" , "More painful or vexed" , "more resentful" .)