Really bad back pain when i take pressure off my back. why is this happening?

Spine Pain Options: This chronic pain in the distribution as you suggested is the result of an irritated nerve or facet joints or other injury typically in the lumbar spine (low back) which are caused by herniated disks, spinal stenosis or degenerative disc disease, etc requiring further evaluation by a spine specialist and may be candidate for facet injections/radiofrequency ablation and epidural steroid injection.

Alternative: Pain w/ pressure ON the back (ex. standing) is more consistent w/ disc inj. or arthritic pain.W/ pressure OFF the back (ex. lying down) muscle should relax. If they can't = increased pain.Also, when muscles relax, vertebrae may spread apart putting increased stretch on intervertebral ligaments.Allowing injured ligaments to stretch may cause pain.Prolotherapy or osteopathic manipulation may help.