<s>[INST] I am having achey pain in the r low back sometimes down the r leg to the knee Can t get comfortable lying down or sitting or even standing. No specific reason or cause. What can be causing this? And how do I rule out other things like kidney issues? [/INST] Hi, If I were your treating Doctor for this case of low  back pain down the your leg to the knee, I would come up with two possibilities, these include: 1- Radicular pain in the leg due to nerve root compression mostly due to back problem and this diagnosis could be excluded by doing MRI for lumbosacral spine2- muscle spasm pain in your lower back due to heavy activitiesKidney disease can be ruled out by doing abdominopelvic ultrasound ,renal function test and urine analysis. </s>