Doctors can not diagnosis what is wrong with me

I am 27 and on hemodailysis.  I had a kidney transplant in 2001 when I was 19 and then 5 years ago my kidney quite working and have been on dialysis every since.

My symptoms started about a year ago when all of a sudden my blood pressure dropped (extremely low) I would get very dizzy when standing and even fainting and when I fainted sometimes would shake.  I also have upper back pain, constipation, numbness, tingling, and I guess a lot of other symptoms that doctors can't explain.  I have had echocardiograms, EKG's, MRI's, Kat Scans. I have been tested for POTS, Adrenal diseases with none of it being correct.  My doctors now after a year are thinking I may have a Anatomic Failure.  I have looked online for answers and I do fit most of the symptoms.  Do you know how I can tell if I have PAF or MSA?  I know MSA is the diagnosis I do not want.  Do you have any good resources for me to check out to help my doctors diagnosis me?  I am just really frustrated because no one has been able to tell me what is wrong ...just keep treating the symptoms.  Can you help me get some information on what to watch for or expect. But I understand this is something that is only for older people?

Thank you for your time