I have experience with both medical school (tried and couldn't get in, as well as married to a doc), as well as graduate school (PhD student now), so I'll separate this into two parts...
Medical School
Applying (and getting in) to med school is not as easy as just deciding to do it and taking the MCATs.
The MCATs themselves will take weeks, if not months, of preparation... not knowing how long ago the OP graduated from university, but in the space of a few years science can change... a lot. Which brings me to my second point... again, not knowing how long ago the OP finished their undergrad... but the pre-requisites for getting the OP's psych degree may not overlap completely, if at all (depending on the institution) with the pre-requisites for medical school.
If the OP hasn't taken them, most medical schools are going to be looking for something like this:
- 1 year of Calculus
- 1 year of General Chemistry + 1 year of Organic Chemistry + other electives
- 1 year of General Biology + Biochemistry + other electives like Genetics + Cell/Molecular Biology
Keeping in mind what I remember from my undergrad institution's pre-med and psychology tracks... there wasn't much overlap between the two (perhaps 2-3 classes were common to both), meaning that the OP could be in for a year or more of taking pre-requisites just to meet the base requirements of most medical schools.
Then, depending on the medical school, most are going to want to see extensive experience in the medical field (eg. volunteering at a clinic, or shadowing a physician) or strong experiences or even better, a record of publishing peer-reviewed research... or even a combination of both. Some schools are going to be heavily focused primary care (Michigan State), others are going to be much more research-oriented, and others are going to want people who excel at everything (grades, volunteerism, research).
Then (yes, there are a lot of "then's"...), keep in mind that medical school itself is 4 years. Then, add 3 years minimum for your residency. Then, assuming you want to do some kind of specialty... tack on another 1 to 5+ years to the end of that. This isn't meant to discourage anyone from the medical profession, but you have to know what you're getting into...
And frankly, there are lots of easier ways out there to make your $150-500k per year salary without the headaches of 60-80 hour weeks, having to be on call, and having to explain to patients the benefits of paying a $20 co-pay to see their physician instead of spending that money on lap dances (yes, true story).
Grad School
Speaking as a grad student in bioinformatics, I can't speak for every other field, but getting into grad school is no walk in the park either.
But, since I was in a similar position as the OP (less-than-stellar undergrad grades), and having seen some of the admissions stuff from the school's side as well, I feel that I can offer some advice.
1) Take the GRE again, but actually prepare and improve your score. Most schools are going to have some kind of cut-off that is a combination of your undergrad GPA, your post-baccalaureate GPA, and your GRE.
There's nothing you can do about your undergrad GPA, but what you can do is take additional classes, or even re-take some of the classes that you did poorly in at your local community college or somewhere similar. Doing this and improving your GRE scores should hopefully "get your feet in the door".
2) Once you have your "foot in the door", you need to distinguish yourself from the dozens, if not hundreds, of your fellow applicants who also have their "feet in the door".
Again, your undergrad GPA isn't going to be your friend... so you need to do other things to help you stand out from the crowd. Speaking as pure science-y student, the answer is: research. Ideally, do research at the university you're most interested in. It's no guarantee of admission, but if you were on the admissions committee, how nice would it look to see a recommendation from one of the major players in your own department? If you do the work and can get your name on a publication, or two, or three... even better!
Finally, put some thought into your personal statement. Don't use it as a forum to explain why your grades in undergrad were so bad... mention it, and briefly explain what happened and the steps you took to better yourself, but don't use it as a crutch. I can give more advice related to the personal statement, but PM for more please... would prefer to not share every detail in public.
If grad school is your goal, let me just say... given my situation, I truly believe that anyone can get in to grad school... you just need to do the work, and find the right fit.