Not to freak you out, and this has nothing to do with any sort of cancer, but you do realise that back pain that causes numbness into the groin, or bowel/bladder incontinence or the inability to pass anything is a medical emergency? As in warrants a quickly timed visit to A&E.

No idea what is going on, but back issues can cause a condition called Cauda Equina Syndrome. That warrants urgent medical attention. It's why doctors always ask you about your bowels or bladder when presenting with back pain.

If it comes and goes, you still need to see a gp asap. Ignored, these symptoms could indicate an infection or a serious nerve compression. It can come on gradually, like it can come and go over a period of months. Doing nothing risks paralysis.