Welcome to ThisIsMS, Lisa. I offer you my standard action plan recommendation:
First, TAKE A DEEP BREATH. You may not have MS at all, but there is always the possibility; it is a differential diagnosis – made by ruling out other possibilities. Very often, it is not easy or quick to diagnose. Before modern, expensive tests were available, doctors used to diagnose MS on the basis of symptoms and if they temporarily worsened when the patient sat in a hot bath for a while. IF you do have MS, you have found many supportive friends at this site. You WILL be able to deal with this – the uncertainty is difficult. We come from diverse experiences and hold diverse ideas. We do not agree necessarily in our thoughts on MS – my personal suspicion is that excess insulin (and resulting insulin resistance) is responsible for many MS (or "neurological") symptoms. You will probably not agree with some of us either; we only ask for tolerance when we express unconventional ideas.
Second, I hope that your doctor is a good GP or internist, that he is compassionate and enjoys being a "disease detective." I tend to believe that if you see a surgeon about a problem, he will find a solution in surgery; if you see a neuro, he will only see the problem/solution in neurology. I just read an article that summed this up well: "doctors are experts in, and only test for, those parts of the body in which they specialize." You say your doctor did a full blood workup. I hope it included these: (1) cortisol level, which can be elevated with stress and cause blood sugar to rise; (2) glucose AND (3) insulin levels (these are two DIFFERENT tests – I think the "fasting blood insulin test" is the most important and it is a relatively inexpensive test (the optimal 3 UU/ML or lower); (4) thyroid hormone levels (TSH, Free T4, Free T3, Total T3, Reserve T3, and antithyroid antibodies). (5) The CRP (C-reactive protein) test (testing for inflammation) and (6) liver tests are also a good idea. Ask for a copy of all your test results for your own file. I suspect insulin involvement and resulting insulin resistance in skeletal muscles causes many symptoms (excess insulin is known to thicken and stiffen smooth muscles; skeletal muscles, too).
Third, if you like to read and if you do have MS, start your reading with two books: Multiple Sclerosis: The History of a Disease by T. Jock Murray, OC, MD, and I think The Multiple Sclerosis Diet Book by Roy Swank, MD, PhD and Barbara Dugan is a good second book to read or even have. You may be able to get these through your local library.
Fourth, I believe insulin is a major player; as a fitness trainer, you eat a healthy diet, no doubt (a good idea whether or not one has MS) –I think the diet should not trigger insulin production. Many people find that diet can influence the symptoms of MS. In my opinion, this means a very low-carb diet --remove ALL trans fats; remove all sugar (including beer, wine, etc. which have sugar), remove all artificial sweeteners, including sugar alcohols like sorbitol, xylitol, etc. (These promote insulin production, too.), and remove white flour, white bread, white potatoes, white rice (in fact, all carbs so far as possible).
My suspicion is that Fatty Liver Disease is also involved in MS (one can be "skinny fat"), since visceral fat (belly fat) secretes cytokines (like poison to the internal organs), which lead to increased insulin, which leads to inflammation which leads to more visceral fat… And the cycle goes round and round. Diet is important; in fact, you may find the account of Dr. Terry Wahls and her dramatic improvement in MS interesting (http://www.TerryWahls.com
All the best to you.