Back pain over half way down (3)
I believe the answer is:
ago
'back pain over' is the definition.
'ago' can be an answer for 'over' (both can mean in the past). I am unsure of the 'back pain' bit.
'half way down' is the wordplay.
'half' suggests halving the letters.
'way' becomes 'av' (short for avenue).
'down' becomes 'go' (I can't explain this - if you can you should give a lot more credence to this answer).
'av' halved is 'a'.
'a'+'go'='AGO'
Can you help me to learn more?
(Other definitions for ago that I've seen before include "In past times" , "Back (in time)" , "Previously" , "Time past" , "(Years) before the present time" .)