Allison, Like all the others who have replied, I sympathize and empathize with ya; your story reads just like mine.
Some advice to get you closer to a diagnosis:
Keep a journal of all symptons, no matter how strange or seemingly "unrelated". This does a few things- it allows you to find triggers to avoid, track trends, and lends a great deal of credibiity to your story when presented to medical professionals. In my journal I also keep a score each day, 1-10, am I chair bound or am I walking normally? Can I feel my feet like I used to, or are they tingling, or are they dead weight? Each "level" of every sympton merits a certain score. Bring this journal, as well as a list of your current prescriptions and OTC drugs/supplements/herbals with dosages to EVERY appointment. Also, when possible, submit a list of new symptoms and any questions you might have, a day or two PRIOR to any medical appointment. This allows the doc to prepare in advance if research is required, and it prevents you from forgetting something important. My neuro actually leaves these in my file so that we can re-visit items as needed over time too.
Find an specialty center (like an MS Center or Institute) near you. You may have the world's most competent neurologist but if he/she doesn't have experience with MS, (or whatever your gut tells ya you have based on lots of internet and library reseach) you may not be getting the best care/diagnoses/treatment. Once you do get a diagnosis, it really helps to befriend the person who sets appointments and can get ya in when needed with little notice. You also need the RN or LPN or NP or whomever does the doc's work 'behind the scenes' to know you and your case. Having a person who knows YOU as a person and not just a case file helps, especially at some of the bigger centers where people drive hours to be treated and the actual doc-to- patient is out of control.
Keep records. Every blood test, every MRI...keep a copy, and when you get to any appointment, leave them in your car but be prepared to go get them, in case the results didn't make it from office to office, etc. (Ask for MRIs on disk, like a CD or DVD, much easier than those silly films. And be sure your MRIs are done with the gadolinium contrast injected.)
Lastly, hang in there! I know it is so terribly frustrating to feel like life is on hold while you putz around looking for some answer that you are probably not gonna like anyway! Focus on the things you CAN do! And while you wait for a diagnosis, treat the symptons. There are drugs out that that help very much with fatigue. There are antidepressants available to help you get thru this period in your life. There are helper tools like canes too. (I hated the cane idea at first, until I found a really cool one that folds up and looks like it might contain some James Bond like weapon!) If your docs act like treating the symptoms is crazy, ask them why they feel your quality of life should suffer while they scratch their heads trying to diagnose.
Keep us posted. Best of luck to you, I'll keep you in my prayers.