Hi, Thesummersun, and welcome. A DO is a Doctor of Osteopathic medicine. They are medical doctors but some use spinal manipulation and massage to help you. They go through four years of medical school and then their residency.
http://education-portal.com/articles/Osteopathy_Doctor_Education_and_Career_Roadmap.html
An Internist has more education than a regular MD.
http://healthcareers.about.com/od/healthcareerprofiles/p/IntMedMDprofile.htm
A rheumatologist who is an MD has gone to school to specialize in this particular field.
http://www.rheumatology.org/practice/clinical/patients/rheumatologist.asp
I personally make sure my doctors are board certified and most are diplomates. They have to take tests I think every year to prove they are keeping abreast of the newest in medicine. If they pass they can continue to keep the title of diplomate. This is how it was explained to me. I also make sure my Internist and rheumy treat fibro patients. There are still doctors out there that are in the Dark Ages when it comes to this illness.
I have a board certified Internist that I use for most everything. I also see a board certified rheumatologist for fibro and ankylosing spondylitis...a rheumatiod-type illness. This type doctor would figure out what is going on with the sedimentation rate...not send you to an Internist.
I think it's good this has happened. You want the most knowledgeable doctor you can find.
Be sure to read Fibro 101...the first thread on the forum. There are links to good info about fibro and you will learn a lot there.
I'm looking forward to getting to know you better. Don't hesitate to ask questions because we are here to help you. Hope to hear more from you soon.
Sherrine