How do you know if a lower back ache is muscular skeletal or a kidney infection ? no fever or uti symptoms.

Sometimes it is hard: To know but a backache due to back problems generally is worse with activity or position and better with rest (mechanical) while back pain from a referred source like a kidney issue or an ulcer is painful no matter what position (nonmechanical). If a history of urinary infections, get checked as they can present with no typical symptoms.