--I do think you need a lower back/sacral MRI, to really visualize possible nerve compression there.

One of the nasty thing about neurologic symptoms is that one can get the exact same symtpoms from systemic conditions (i.e., diabetes, autoimmunities) that one can from more local ones (i.e., spinal compression), and these can be felt in the exact same place even if they don't "begin" there.