Back Pain since 1 year. Relief) ?

I have back pain from lower back upto mid spine area ( vertical) and also along with belt from one hip to other( horizontal), forming symmetrical inverted cross.This pain is since feb 2017, when I started 30 min to 1 hour walk post my workhours, which I did 3 months and discontinued it because I developed the said pain,which since then had increased both  horizontly and verticaly. I consulted two orthopadic doctors and have done Xrays tests twice ( june'17 and Jan'18) and recently undergone MRI. All reports are showing no anamoly as per doc.Doc also recomnended test for Vitamin D and B12. Also I have been going for physiotherapy sessions for 3-4 months.I have shown to 4 -5  physiotherapist too. But all in vain. My question is what should I do now: 1. Should I consult some other doc? 2.Should I continue physiotherapy (which has rendered little to no healing hitherto but some temporary relief)?also advised by doc to discontinue. or 3.Should I continue with same Doctor. ...please Suggest.