there is an extremely more likely connection to a disc problem causing your twitching etc, than als causing it, and no, als will not cause the type of back pain you're describing, but it is CLASSIC for disc problems.
I've been there, done that. Had at one time 7 herniated discs at the same time, (4 in lower back, 3 in cervical spine) absolutely know the feeling. and I've had bursitis - at the same concurrent time. and the bursitis hurt over where you're describing....and... before you ask, this was all years and years and
years before any of my current illness, which was bulbar onset, and I have no back pain now.
To diagnose the back pain you need a complete mri, and to see a specialist in that field. I went through the series of epidural shots (twice, total of 6) then had some muscle repair to my abdomen, and after the surgery my back never ever bothered me again. other than middle aged lady aches once in a while.
good luck
