I don't think it's that anyone necessarily "threw you under the bus" as far as letters of recommendation. I do agree that LOR's from types such as attorneys
and chiropractors may not be that helpful. The chiropractor one may be OK depending on who is on the adcom and whether he/she feels open minded about chiropractors or not. In general the medical community is quite conservative and they probably prefer letters from professors and at least one letter from a physician if you can get one.
Definitely do practice interviewing skills, and know what your answer will be to some of the typical interview questions, such as why you want to do medicine, what are the important current issues in health care reform, what are your best/worst qualities or strengths/weaknesses. Interviewing well is a skill that you can learn.
Definitely do call up the schools where you got interviews this year, say that you really liked their school, you were disappointed you didn't get in, etc. and then ask what you can do to improve your application.
Improving the MCAT score would probably help, but if your score drops it could hurt you so if you plan to do it I would start studying now.
You need to keep on with medically related volunteer work.
Definitely do have someone review your essay...though it may not be the issue.
One thing you have to guard against is being seen as the "average applicant". Try to think of things that make your application unique, that make you a good fit for particular schools, etc. so that you can sell yourself.
I do not think you should bail for the Caribbean at this point. They will still take you in 6 months or a year if things turn out badly for you up here, but it's suboptimal. It makes it much harder to get a good residency, and the education will be equally or more expensive down there. The 3rd/4th year hospital rotations are really important and I don't think premeds fully understand how important they are, and some of the Caribbean schools just don't really have good ones or well organized ones (though SGU is probably OK in that regard).