Have you looked into any AmeriCorps programs? I have done two, and have a few selected as possible back up plans. They are nice because you can still travel a little bit. My first program was NCCC which is all traveling; new city/state every 6 weeks or so. My second program was a state national program in Washington State. I am originally from Michigan so I got to spend a year out there, pretty close to Seattle and I was able to work with at-risk-youth.
You do not get paid much, but generally you are able to live (like Peace Corps from what I understand), I was actually able to save a little money in my State National Program in WA state and came home with some padding (not much, but enough to merit mentioning) in my savings account. But another benefit is a scholarship you get when you are done. Upon completing the program you get a $5,000 (somewhere in that range at least, I hear it has changed a bit since I've done it) scholarship that can be used to pay back loans also.
So, I have a few of those kept in mind. They are a year so my backup plan would be to do one of those and while doing that begin the grad school application process. I haven't started those apps yet because they are just a little bit shorter in nature of the application process. But like I said, the AmeriCorps programs are one year and the application process is much shorter and less bureaucratic (although still a bit bureaucratic, it is still the gov't you are working with), you could then get a scholarship and during your time in AmeriCorps work on post-baccalaureate med program applications while potentially working in public health field doing volunteer work of some sort with AmeriCorps and then you don't even have to tell those programs you are simply applying in case Peace Corps doesn't work out.
If you are interested in the possibility of an AmeriCorps program but have any questions, it was a few years ago I did both of mine, but I loved them and wouldn't mind talking with you about it.
Of course AmeriCorps is not for everyone and if you have your heart set on those med programs if Peace Corps doesn't work out, I'd say go ahead and apply and don't tell them quite yet about Peace Corps because as far as you know right now...well you don't know anything for sure yet, so maybe wait to tell them until you have just a little more information.
That is just my advice though, I'm sure you will make the right decision for you.
I'm also a bit worried about med clearance. I worked two jobs this past summer, one of them simply to put money away for the medical portion of the application since my "insurance" might as well be no insurance. I'm worried about spending all that money on med clearances and then one of my last steps or something they say, sorry bout your luck but we can't accept you. All that money would be thrown away!!!!! But it is a risk I knew I would have to take and one I saved for, but it still doesn't make it less painful thinking of spending all that $$$ to still be potentially turned away.
If you don't feel like talking about it on the internet with a complete stranger I will understand, but just out of curiosity what is your medical condition you are concerned about? I don't have any specific condition, I'm just concerned about all the bumpiness I hear that goes along with medical. I don't have any conditions, but who knows what might cause PC Med staff to decide to say no...I've unfortunately read some pretty sad blogs/stories/incidents with that happening