Suddenly tailbone pain?

I've been using my bike to commute for about a decade. I've had the same bike for 8 years and the same saddle for 5 years (both are still in good shape, i've already checked the seat for breakdowns in the material and it's fine, it has a 10 year warranty).
For some reason, for the last couple of months I've been getting horrible tailbone pain if I ride any farther than a mile. No accidents, no falls, I haven't injured my tailbone as far as I know. Resting until the pain goes away doesn't help, as soon as I get back on the bike, it hurts again. I don't know what to do. It's just started happening out of nowhere, it's not like I'm a newbie, I would think if I was going to have tailbone problems it would have happened 10 years ago when I first started biking, not suddenly start for no apparent reason after a decade of riding 5+ miles a day 3-4 times a week.
Suggestions?