with pain in lower back these are strong possibilities.Kidney
stone, any kind of malignancy, Infection yes but with investigation like Ultrsonography,MRI of abdomen,Cystoscopy
,casue should be clear but we sould also rule out Tuberculosis?,any history of drug ingestion, and any kind of Connective tissue
disorder also should be looked in to. With limited information exact cause can not be said with certainty.
Consult a uro surgeon.