There is no proper test for MS! MS is diagnosed by ruling out things which MIGHT be MS symtoms...so far, you have ruled them all out. Stop worrying and start counting your blessings!
MS isnt a joint disorder- its a central nerous system disease....its found in the brain and spine- there is no single test which proves MS....but, the tests that you have had are showing that it isnt. Because you are not showing any symtoms which scream Neurological- consider yourself blessed and fortunate.
Im not trying to make light of your situation. Unfortunately, anxiety is a very real disease as well....and you might be experiencing some panic disorders on top of it, causing you to have some of your symtoms. My advice to you, is treat what is happening to you exactly like you have been. Talk to your doctor about each and every episode that you experience, but TRUST your doctor...if the tests and exams prove negative, then TRUST him (or her) that they are telling you the truth and try NOT to worry. Possilby some anti-anxiety medication might help you to cope alitle bit better. Those of us who have had to cope with MS diagnosis's, have sometimes been put on Xanax, or other similar drugs with success. I myself, have been on Xanax and have had to resort to using it when things get tough....theres nothing wrong with using a medication the way its supposed to be used, to help you get thru rough patches.
I wish you only the best...