Good Day and thank you for being with Healthcare Magic! Cystitis could be a local problem in the bladder or could be coming from the kidney. I would recommend getting a kidney and urinary bladder ultrasound to check for any anatomical abnormalities that may be corrected. Cystitis can be caused by abnormality in the the defense mechanisms of the body. I suggest drinking plenty if water to flush away the bacteria. Tetracycline is not a good antibiotic and I usually prescribe ciprofloxacin but you may need a prescription to purchase it. I hope I have succeeded in providing the information you were looking for. Please feel free to write back to me for any further clarifications at: http://www.HealthcareMagic.com/doctors/dr-manuel-c-see-iv/66014 I would gladly help you. Best wishes.