During uti its common to have fever due to infection in body. when ever there is infection the body s immune system fights against them and it responds as increased in body temperature. But along with this due to fever patient will have generalise body weakness and will have more pain for the muscles which are already weak. In your case it may be spinal muscle which are week and so that patient is having back pain. Along with this pain if patient also have disc related issue at lumbar spine then he will also have symptoms at thigh level with radiating pain or increased sensitivity in thigh muscles. Here I suggest you nothing to worry just finish your antibiotic medication course for uti and then check, most probably all symptoms will go away and later you should do spinal strengthening exercises. But if still back pain and increased sensitivity at thigh level continue then consult orthopedic and take mri of your back to rule out issues with lumbar level. Here based on report orthopedic will guide you for further treatment planning. You can also check with physio for physio treatment, postural correction and spinal exercises for early recovery. Take care.