Reminder from yours truly to doctor (4)
I believe the answer is:
memo
'reminder' is the definition.
(thesaurus)
'yours truly to doctor' is the wordplay.
'yours truly' becomes 'me'.
'to doctor' becomes 'mo' (medical officer**).
'me'+'mo'='MEMO'
'from' acts as a link.
(Other definitions for memo that I've seen before include "Written business message, in short" , "Short note or message" , "diplomatic communication?" , "It will remind" , "In brief, a note of events" .)