Thanks for writing in. Recurrent kidney infections can be caused by infections including STD, abnormality in the form of urinary tract, due to reflux of urine from the bladder, stones obstructing the urinary tract, immuno compromised conditions etc.
Don't worry, the doctor might have scheduled you for an ultrasound to look for any anatomical abnormality if present in the urinary tract or for any stones in the urinary tract which might be causing obstruction there by subjecting the kidney to recurrent infections.
In both conditions surgical treatment might help. Also check what the urine sample report says.
I would also suggest to get a check of random blood sugars for diabetes, as this a common cause of recurrent infections.
Feel free to post if you have any doubts.