Only when laying down I have burning in my lower back but I have been having blood in urine but not everyday and tested negative for UTI what's wrong?

Back pain /hematuria. The symptom profile described could be associated with stones of the urinary tract or possibly a kidney infection. The negative urine makes an infection less likely, but an infected urine trapped behind a stone would not be detected. It would be wise for someone with those symptoms to be evaluated through the emergency department so rapid evaluation and initiation of treatment can be carried out.