Hello. Need ideas please?

12 yr old Lab mix, very strong gait before leg injury. Full rear right amputation.  On carprofen and occasionally gabapentin.  After surgery for 2 weeks he was using remaining leg well albeit with our limitations.  eventually we took a flat 1/4 mile walk and he did very well but tired near the end.  Now 4 weeks out he can hardly walk after about 1 minute. Rear sags, spine curves towards missing leg, remaining leg walks sideways. Vet says possible nerve impingement.  Here is vet report:  thanks for looking at!😄
-Left stifle: moderate periarticular thickening, mild crepitus on PROM, reduced stifle flexion with firm end-feel, stifle is stable to tibial thrust
-Left hip: mild hip joint pain on joint compression and joint mobilization, pain on end-range extension and abduction
-Left Hip Flexor mm: moderate pain on iliopsoas mm. stretch, mild tight bands on palpation of caudal psoas major mm. belly, comfortable on palpation throughout iliacus to insertion, mild to moderate muscle spasm on palpation of proximal rectus femoris
Axial/Neuro:
-Cervical spine: normal PROM and AROM with no palpable pain
-Thoracic spine: mild muscle spasm on palpation of caudal thoracic paraspinals at TL -Lumbar spine: trigger points just caudal to the TL and at L5-L7 bilaterally
-Lumbosacral junction: pain on ventral pelvic tilt, pain on direct DV palpation of LS space