Hi believeinray,
First off, a 690/Q45 is a really strong Score, so it could be enough to get you into your first-choice School. As such, a retest might not be necessary. Your Admissions Expert brings up a good point though. Many Business Schools view an Applicant's Quant Scaled Score as an indicator of how that Applicant might handle the 'academic side' of the Program - and a Q45 won't impress anyone. That score implies that you did fairly well on most of the "math" questions that you saw on Test Day, but you missed out on a block of 'strategy-based' points. This is meant to say that by focusing on Quant Tactics, you'll be better able to increase your GMAT Score AND better impress how Business School Admissions Officers will view your potential to handle their respective Programs.
Before I can offer you the specific advice that you’re looking for, it would help if you could provide a bit more information on how you've been studying:
1) Since you're currently a medical student, how many hours do you typically study for the GMAT each week?
2) Were those 2 practice CATs the only ones that you took over the last 3 months? On what dates did you take EACH of your CATs/mocks and how did you score on EACH (including the Quant and Verbal Scaled Scores for EACH)?
3) Do you have your next Test Date scheduled yet or are you generally thinking about retesting at the end of March?
GMAT assassins aren't born, they're made,
Rich