You do know that MD/PhD programs split the med school and grad school portions, right? Unlike in grad school, you don't do research while taking classes in an MD/PhD program, so already that's less stressful. Many med school professors have also told me that med school classes are easier than grad school classes, so that's another thing you just made more stressful for yourself (also the fact that now you have to take both graduate and medical school classes).
But the part you really screwed up on is that by planning to apply MD-only to med school you now have to shell out hundreds of thousands of dollars to become a physician scientist. There's a reason why most MD/PhD programs (and PhD programs in general) waive tuition: No one in their right mind would ever pay to become a scientist, because you will NEVER see a return on that investment. MD programs are priced with the assumption in mind that you'll become a specialized physician and make at least $200k/year. As a scientist you'll be making about $40k while you're in post-doc limbo, $50-$60k as an assistant professor, $60k-$80k as an associate professor, and $90k-$110k as a full professor. Sure, there are private companies, but I assume that isn't what you want since if it was you could already have a job at one of those companies with an MS and be earning about the same salary you'd have with a PhD at those same companies (this is, of course, assuming that you have expertise in a field that biomed companies want like biochem or microbiology).
I have heard of scientists going to med school after getting their PhDs. In fact, I know one woman who got her PhD in physics and is now working on getting her MD. Thing is, all of those people only went to med school after they had no luck getting jobs and/or funding as scientists, and thus were planning on becoming physicians only, not physician-scientists.
Finally, consider that the MD/PhD is effectively overkill for any kind of research. Both MDs and PhDs can and do conduct basic, translational, and clinical research. You don't need the MD/PhD. There are reasons why a person might want to get one, but if you already have a PhD there's absolutely no point in getting an MD unless you want to change careers completely.
tl;dr - Don't waste your time with the MD unless you want to be a physician.
