I have been experiencing pain on the left lower side of my back, that travels down the back of my leg. I can lay or sit and it hits me. It's not a real sharp pain but a throbbing pain that grabs then release, but constant. This been going on for 2wks now, I just got treated for an UTI finishing up the meds today. So I was wondering if its my sciatic nerve or dealing my kidneys. Can you please help me understand?