Donnybrook's personal nurse regularly provides motivation (7)
I believe the answer is:
impetus
'motivation' is the definition.
(thesaurus)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for impetus that I've seen before include "influence" , "Drive" , "Thrust" , "Incentive - time's up (anag)" , "Driving force, forward movement" .)