Usually neuros will start with the brain MRI because lesions most often show up there first. A spinal MRI may be ordered later if nothing shows up on the brain MRI, or through other testing.
As Rhonda said, though, there are lots of disorders -- some of the neurological, some metabolic -- that "look like" MS on the outside. So the doctor will want to rule out things like thyroid problems, diabetes, other autoimmune disorders, infections, all sorts of other things, before deciding that you might have MS. You may be sent off to have a spinal tap (or lumbar puncture), for example, or have a bunch of blood drawn to look for some of these other things, or have evoked potential testing done, where your brain waves are measured.
I'm sorry you're having problems, and know the waiting is a challenge. Don't be afraid to ask questions; we'll try to help.
Welcome to the board. As you have probably figured out, we will not diagnose you or even tell you if we think you have MS. There are just a ton of things that can look like MS. You will need to wait on your doctor and see what he says and what the MRI shows if anything. My doc started with brain MRI then eventually went to neck and back. I am not sure why they always start with the brain but that is pretty standard. From what I understand, and I am by no means an expert, most often lesions show up in the brain. Some people have brain lesions and spinal lesions. It supposed to be quite rare to have only spinal lesions. So the brain seems to be a good place to start.