I Have Recurrent Uti Infections, History Urosepsis And Still Have

i have recurrent uti infections, history urosepsis and still have 2 stones in left kidney. today I have stinging pain in left kidney and I think another uti infection as have letter from doctor from urine sample left Saturday at the clinic for testing. why if I just finished nufloxin antibiotics can still have uti after just finished the course?