First and foremost, as Doc Admin points out, get an honest gauge on your motivation and ability regarding a medical career. If, at that point, you are still gung-ho, then do not stop until they tell you to go away and never come back!
Also, I am at one of the osteopathic medical schools Doc Admin referred to, and I am delighted with my choice. Many of the people in my class had their choice of several MD and DO schools, and chose to come here. With the admissions cycle, DO schools really focus in on the whole applicant, and you MIGHT be able to get away with a lower GPA or (NOT AND) MCAT if you have other facets to your application which make you attractive.
At a DO school you will learn everything your MD colleagues learn, plus neuromuscular medicine and manipulation (somewhat similar in concept to physical therapy, etc.). Indeed, as a DO, you can go into any facet of medicine that inspires you, and in some circles, you are actually at an advantage as a DO (with the additional emphasis on physical medicine).
For example, this year's incoming class at Harvard's Physical Medicine and Rehabilitation Residency has 6 slots. Five of those incoming resident physicians are DOs.
However, I am interested in an IM/PSY or FM/PSY combined residency, and others are going into Surgical specialties or Emergency Med. Whatever you want to do, medically, you can get there from here.
(OK, I will put down the DO pom-pons now.

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The main thing is, if you have to take some classes over, or you must take the MCAT a second time, but you really want to be a doc, then don't be afraid to give it your all. Just make sure you REALLY want it, because it is a long haul, and it isn't easy.
Good luck, and keep at it.
