I have a problem of re current urine infection from last 5 year . i done all my test and cystoscope done. couldn't find reason why?

Recurring cystitis: Assuming that you've had a complete urologic work-up and it was normal, it is likely that your bladder lining is simply prone to bacterial infection. More of a problem when a women becomes sexually active ( that is when bacteria get from vagina to urethra and bladder). Urinate after intercourse and try drinking a daily glass of cranberry juice. You may need low dose antibiotics for prevention.