Since this started about three months ago, there is a chance that this is a relapse and it might get a bit better, especially after you start the Rebif.
When I was first diagnosed, my doctor told me that Rebif was very powerful and if I started to have severe symptoms, such as those affecting vision, they would use that. I took it for about five months and the shots were the easiest of any I took to date.
They might add an antidepressant at some point because MS can have depression as a symptom and interferons can have that as a side effect as well.
It sounds like your doctor is doing all of the right things so far. If you were having mobility problems that might make them want to look at the spine.
God bless you, I hope you'll feel better soon.

This is a good place for support.