Hi Cathy,
Glad to have you here with us, and congrats on no new lesions - or antibodies that's wonderful!
What was viewed by MRI after the fall? Your full spine?
I'd say the burning can be your MS, even though you have no new lesions. But you bring up pain in your lower back, so I understand why you are looking into something structural.
Did those muscles relaxers help anything? They wouldn't touch pain associated with the central nervous system. We have a couple great health pages you would enjoy reading on parathesias, and pain. Here's the links:
http://www.medhelp.org/health_pages/Multiple%20Sclerosis/Paresthesias---Things-That-Go-BUZZ-in-the-Night/show/378?cid=36
http://www.medhelp.org/health_pages/Multiple%20Sclerosis/Nerve-Neuropathic-Pain---A-Primer/show/371?cid=36
If it were me, and I was doubtful it was my MS, I'd get a 2nd look by an othopedic, or spine specialist. If it turns up nothing, you'll know. Then you and your neuro can look into taking something to simmer the nerves maybe? I'm on baclofen for spasms, but some have had relief from neurontin.
Hope to see you around. How are you feeling otherwise?
-shell