Had urine infect now getting lower back pain. scans and test come back negative, lethargic and emotional what could it be?

UTI, LBP : I assume the scans are of the kidney to check for infection. Did they do a culture and tell you the organism ? i have seen UTi symptoms with interstitial cystitis ( usually no growth)and also in women who have vaginal infections with mycoplasma / ureoplasma so would check that out as well . In addition ensure you did not get a secondary yeast infection from antibiotics for UTI f/u/ w/ MD