I've had inflammation and sensitivity at the very end of my tailbone for ~1yr. it's as if someone put a 1" diam 1/8" hemisphere marble there. concern?

Coccydynia: The coccyx is a piece of cartilage at the tip of your tailbone and is very tender once it becomes injured or inflamed, and that tenderness can last month's to years. It is more of a nuisance disorder than anything serious,but if you still have concerns see an orthopedic specialist for evaluation and advice.

See below: Sounds like you have coccydynia or 'tailbone pain'. This can occur with trauma to the tail bone, abnormally positioned coccyx, or poor sitting posture. Try using a good lumbar support to help shift your pelvis forward. This will put the pressure on your ischium. (bottom part of pelvic bone), and will shift the weight off of your coccyx (tailbone).