After a good viewing and poking and probing by a PA today, I was diagnosed with a cyst, and told to sit in a hot bathtub for about ten minutes, twice per day, and it will go away. I think it's already slightly smaller than it was, so that's good news also.
And I agree about not asking about medical advice on the internet. It reminds me of a parody thread I once read at another forum with a title something like "Trapped...under car...can just barely...reach...laptop"
But, I thought this might be bicycle-related. That's why I posted this here. The PA agreed that cycling probably caused it.
Having gotten all kinds of good (and accurate!) answers, I shall now sprint with youthful vigor back out of the old-timers' forum before I get whacked by any more canes.
Thanks again to all those who took the time to assist the brash youngster who snuck in. I'll be back for my official membership card and key to the bathroom in 2018 (I hope).