Hello! and welcome!
It sounds so scary, and walking or running a mile in those shoes feels horrible some days. First, let me say BREATHE! take in some oxygen and breathe. You passed the MRI and that shows that you dont have some raging infection/brain tumor/bleed...so, the rest of the answer come slowly. sorry to say.
There are more than 100 diseases that can "mimic" MS symptoms including brain lesions. Lyme, Lupus, Sjoghrens, B12 def, and so on. the list is impressive. The MDs generally do this as a "rule out" style medicine. They look at those things that CAN be proven. Vit def is one. Simple blood tests will reveal such things. Lyme should be sent to a special lab, and even if ruled out there are many false positives. If all else fails, they may retest you. Sjoghrens is a lip biopsy. The list goes on. Once they reach thru those 90 or so diseases, they are left with a handful that CANT be proven thru blood, MRI...MS is a disease that we get tagged with generally when they cant prove you have any of the other diseases. Some of us have very typical patterns in the brain of lesions that blink and light up to the neuro who says WHOA! yep! thats MS. While others have NO lesions, clean spinal taps, and mild symptoms.
If you have an MD who you feel is listening to you. Is continuing to look for an answer and isnt just dismissing you as "over stressed" or "overly sensitive" then hang in there while he digs thru the pile.
Its always a GREAT idea to go to an MS center. Even if you have to travel to get to it. Many folks travel, and go just once for a diagnosis or rule out and use a local neuro for their care. They are expert at taking those little nuances and saying yes, or no its an MS thing. They rule these things in and out all day everyday, and its the happening place to be if you think you have it.
hang in there, let us know how you are getting on.