I have an improvement over my response in another forum.
The patient's pre-existing jaw pain had begun to intensify a week prior to her examination/appointment/visit.
Why do you need to start with it that way? It's not natural. Among other things, we'd be much more likely to say "jaw pain" than "a pain in her jaw" and in even in that order, it would be "pain in her jaw."
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.