I found that my lower back was sore today while standing then found unexplained bruising along my spine.

Medical check up nee: You need to have a medical check up from your doctor. Bruising can be from trauma/injury but you will know if that is in the picture or not. Unexplained bruising indicates possible bleeding under the skin for which there has to be a cause. Your doctor can check/examine you to find the cause of bleeding which will require blood tests including CBC(Complete blood counts) and some special blood test