I have had this aswell. I actually have it on both sides, both started at very different times. My dr refised to do any tests for it because it is almost always a lumber issue. I went to a chiropractor and she did an excellent assessment. She recommended me to strengthen my core, exercise, and lose some weight around the belly. She also recommended acupuncture. I have started exercising, but I don't have the guts to try acupuncture. I have always had lower back issues. I did see a neurologist for a different reason and I mentioned to her about me sciatic nerve, since it can cause me numbness, she recommended the same treatment as my chiropractor.
I have had sciatic problems for a few years now, I am sure if it was cancer or a tumor, I would be going down hill. But that doesn't seem to be the case.