I'm a 44 year old male and am experiencing this for the first time. Good to hear that others are confused about it as well. In general I am very healthy and not the least bit hypochondriac (I was wondering for a few days if I was imagining it). The pain has been on my stomach and back, mostly on the left side of both (though it does seem to migrate a bit from day to day). It's been about 5 days now; I have not visited a doctor and it's the first time I've experienced this.
After thinking about it, I am a person who does not sweat a lot, even when exercising, and in general I probably don't stay hydrated enough. So today I decided to drink a lot of water and work out on an orbiter and see if profuse sweating affects it.
I noticed that, while exercising, there was almost no pain at all. After finishing, the pain returned but doesn't seem as intense. The interesting thing I noticed though is that the painful areas did turn red after exercising; the red did not coincide exactly with the painful areas but clearly my left stomach and left back area were red, generally right around the painful areas.
Perhaps others might try this and check again with their doctors, if they have this visible symptom. I have not been to a doctor yet.