How horribly difficult for you - it is impossible to imagine what it must be like, but I am so sorry you have to deal with this.
As you say, getting a diagnosis is in a way a relief, but I still hope the second MRI won't confirm the results. You would still need to find out what is going on with your body, and that is incredibly frustrating when the doctors won't believe you. (That I can relate to, and I'm sorry you are having to go through it.)
Keep us posted - we're all here for you if you need us. I'm glad you have support in RL as well.