Does your brother have any prior history of fever, sore throat or other flulike symptoms ?
Did the symptoms start abruptly?
Any associated trauma to the area (like during contact sports)?
Any history of prolonged intake of medications?
Any recurrent urinary tract infections?
Some kidney stones may not be visible in ultrasound. A kidney,ureter and bladder CT scan will be able to help.The CT scan is far more sensitive and enables one to determine presence of stones .
I suggest that your brother have a thorough assessment done.Further evaluation is necessary.A cystoscopy and a referral to a gastroenterologist may help.
Give your brother plenty of water.Allow him to maintain mild daily exercises to improve circulation.