What is the difference between lower back pain and kidney pain?

I tore my ACL, meniscus and dislocated my knee a year ago. I have been limping/walking differently since then (limping before and after surgery and just walking f'd up because I'm relearning how to walk normal again). Well my knee has been getting a lot better but on the 4th of July I was told I have a blood clot in my leg and now am on Coumadin aka blood thinner. Recently I have a very dull achey lower back. I don't have dark urine in fact it is almost clear so I'm pretty sure there is no blood in it. So is it because my walking has been out of whack or because of the blood thinners? I get my blood drawn next monday and I plan to tell the pharmacist to see what she says. I just want to hear what you all think.