Thank you for your query at DoctorSpring.com
I have read your query with diligence.It looks from your details as well as from MRI that you may be suffering from compression of nerve in your vertebral column,Your MRI describes that-
1.There is protrusion of disc in spinal canal between the lumber no.4 & 5 vertebrae.This disc is only compressing the covering of spinal cord but not the nerves.
2.Between lumber no.5 & sacral no.1 vertebrae there is abnormal displacement.This creating small defect in part of vertebrae bone.There is displacement of LUMBER 5 VERTEBRAE OVER SACRAL 5.This is producing compression over nerves exiting between these vertebrae.
Your present back pain is due to this displacement.You should be alert.This is early stage & can be controlled by conservative means.You cam ask from your orthopaedic doctor for this is in detail.If this progresses then this may need surgery.
Hope this will help you.