(((((Judy))))), I went through the same thing, in the PT hospital. Sooo sore, sooo exhausted and sooo weak. It didn't seem to be working either, but after awhile, thru the pain and weakness, my legs did get stronger and I am able to transfer to my scooter to couch to potty to whereever easier now.
Your legs will only get so much stronger. Unless you are early in your RRMS disease, you will probably not go back to normal.
I think you are having an attack and I believe pt is the only way you are going to get stronger.
Ask them to do an ultra sound with warm then cold packs for lower back therapy, before PT and that may help to quiet your back during your exercises. Years ago, they did that for me and it sure helped me during PT and felt wonderful.
Hang on, don't give up..