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. It can be due to chronic UTI or vaginitis also.
I would suggest that you consult your Doctor so further investigation can be done.