Basically, Causes can be divided according to the affected organ and they are
Kidney conditions (infection, pyelonephritis,
kidney stones, polycystic
kidney disease), Bladder conditions (cystitis, bladder polyp, bladder tumor), Urethral conditions (Sexually transmitted diseases, urethral injury, vaginal inflammation), and certain bleeding disorders
I feel that without clinical examination, pinpointing a diagnosis is tough. Also a complete urine examination and culture may be required.