Career Changing Guidance

I am currently 25 and graduated about a year and a half ago from college with a degree in history from USC. My final GPA was a 3.0. I’m currently working in an real estate financing job and am not enjoying it. I don’t feel challenged and have always considered persuing medicine and now am seriously considering trying to go to medical school. However, I am sort of at a loss on how to go about it. I didn’t take any of the pre-med prereqs in college, other than some english and a semester of calculus and chem, and didn’t really focus on my GPA since I had a pretty much guaranteed job when I graduated. I was always good at science in highschool and took all the AP science classes. My predicament is that most of the post-bac programs require a higher GPA than I graduated with. I basically need a way to take all the prereq science and math course and boost my gpa. I don’t know if that would require going back and getting a second degree in biology or something. I would really appreciate if anyone has some advice if they found themselves in the same situation or have gone through the same process.