your symptom indicate artiritis of lumbosacral spine with lumber radiculopathy
,x-ray LS spine shows only the bony pathology and gives some clue regarding intervertebral disc
and as it is showing straightening of spine so you need to under go mri LS spine which will show the status of disc and neural foramina.Regarding the curvature if some thing comes like disc prolapse
or ligaments hypertrophy which can be operated then doing physiotherapy
can restore your curvature.