What Causes A Feeling Of Weakness In Legs?

i am suffering from lower back stiffness and chest stiffness and mild breathing difficulty be a sign of AS. . HLA B 27 positive. RA negative. uric acid normal. hb 11.5. age 28. male. pain for last 8yrs. mri, x rays normal. esr, crp normal. weight 65.5 kg. height 5 8 . taking painkillers from last six yeras muscle relaxant prescriptions. stiffness between shoulder blades always there on getting up after lying down for 5 minutes or more. feel it only pain and stifness. sometimes feel feverish and kind of unwell. dizziness also and kind of weak feeling in legs. strength and all is ok...but its a feeling of weakness. what could this be? i am tired of confusing diagnosis and this sick feeling.