Experiencing difficulty. but evidently not off one's trolley (2,3,4)
I believe the answer is:
in the cart
'experiencing difficulty' is the definition.
('in the cart' can mean in trouble)
'evidently not off one's trolley' is the wordplay.
I cannot really understand how this works, but
'not' could be 'nt' (synonyms) and 'nt' is present in the answer.
'trolley' could be 'cart' (I've seen this in another clue) and 'cart' is present in the answer.
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
The remaining letters 'he' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
'but' is the link.
(Other definitions for in the cart that I've seen before include "experiencing difficulties" , "behind the horse" , "Situated awkwardly" .)