Hello, Im sorry to hear that! Im a psychologist and therefor do not know alot about back pains but, It seems like you recently discovered the dent? What could cause dents in the lower back could be spina bifida occulta, a problem wihere the spine has a small defect from birth sometime associated with an area of darkened or hairy skin overlying it. In the majority of situations nothing needs to be done about it. And then it is something called spondylolisthesis, its a slip of one vertebra over the other wich could cause a bump. The pain could be because of instability or nerve root entrapment, Nerve entrapment causes pain by trapping nerves and may need surgical decompression.But it could also be some sort of an hip problem can make the spine curve a bit more, and give the impression of a dent in the back. But what you should do is to visit the doctor or if you are in severe pain you should ask somebody to drive you to the hospital where they should be able to do an x-ray.I wish you get healthy very soon! Regards Hans johan