I have had a dull ache in the right kidney for about 8 months, it just does not seem to go away, could a low grade kidney infection last that long? I have no other symptoms, no fever, no blood in urine. Could it be a real slow passing kidney stone? or has anyone ever heard of a tumor on the kidney? would that cause a ongoing pain to the kidney? Could it be a muscle? it seems like it is in the kidney, could it be the liver?