dear friend the flank pain which radiates from back to pevic area or urethra and sometime may cause burning/difficult urination is suggestive of kidney stone. you can perform simple test that is urine[routine & micro] at pathology lab nearer to you. in urine rbc will increased and if infection in urine it will also show pus cell in urine examination.likewise kidney stone and infection can be diagnosed. x-ray can also fine stone in kidney/ureter,but sometime it can be missed in x-ray. so you can do sonography of abdomen.it is costly but it is better to diagnose than other test. you can do sonography in trust hospitals in your city which charges less than private. hope this answer will be helpful to you. for more queries plz don t hassitate to ask. get well soon