A master's does not matter as your undergraduate GPA is what counts for cutoffs. Spend your time on undergraduate grade remediation.
If you are willing to consider DO, which is good since DO does grade replacement, do the following. Look at your transcript carefully (put it in a spreadsheet) and see what would happen to your GPA if you retook all classes in which you made a B- or less. If you have a few F's, this will rapidly improve your GPA. Combined with the fact that you haven't yet taken any of the pre-reqs, I bet you can get your GPA in a pretty good range in a reasonable time-frame.
If you have many scattered mediocre grades, i.e,. lots of B- and C+, this will not work as fast, so it is transcript dependent.
