On top of what's already been said:
Information for
how to apply is found here:
https://students-residents.aamc.org...ical-school-amcas/how-apply-med-school-amcas/
The AMCAS application opens for submission on June 1. You can take your MCAT whenever you want, ideally before you apply. Most people take it the winter or spring of the year they're going to apply. (e.g. people applying now for the 2018-2019 cycle took it in spring 2018 or winter 2017-2018).
As far as
MCAT materials go, most people use TPR, Kaplan, Examkrackers, NextStep, Khan Academy, and AAMC resources. At the end of the day, your success on the MCAT depends a lot more on you than it does your resources. Any of the above are excellent options. I personally used Kaplan and scored a 519.
I
studied for the MCAT over one summer while working full time in a research internship. I took 7 full length practice exams throughout the summer and went over each exam in detail afterwards. I also read through each Kaplan book multiple times and took notes, and watched Khan Academy videos as a supplement. Studying during the school year is a little different, since you will study less each day but have longer to do so. Just make sure you balance MCAT studying with school, at any point you feel like you're sacrificing one for the other it's time to make some changes. Your current GPA is a tough sell to a lot of MD schools, and you can compensate with a higher MCAT. However, you certainly don't want your GPA to fall further while preparing for the MCAT.
There's nothing wrong with taking a
gap year or several, however, I personally don't think getting a post-bac degree is the most efficient use of time. Instead, maybe consider doing clinical work, volunteering, doing research, etc to boost your application.
Best of luck!