Little person — bit of a pain after short time (5)
I believe the answer is:
titch
'little person' is the definition.
(informal term for a short person)
'pain after short time' is the wordplay.
'pain' becomes 'itch' (I have seen 'Irritating pain ' mean 'itch' so perhaps 'pain' could also mean 'itch').
'after' is a charade indicator (letters next to each other).
'short time' becomes 't' (abbreviation; 'short' asks for an abbreviation).
'itch' after 't' is 'TITCH'.
'bit of a' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for titch that I've seen before include "Small person" , "Little one" , "small one" , "Small man (colloq.)" , "One's very short" .)