The verdict is: stress fractures. Yes, plural. The right one is in the lower tibia and was the cause of constant pain, enough to get me into the doctor. The left one was a surprise :( Thankfully that one doesn't hurt and I never noticed it.
The good news: The prescribed remedy is rest. I saw online that serious stress fractures may sometimes be put in casts. Thankfully this wasn't the case!
The even better news: I can bike. Although I think the doctor's idea of stationary biking and my idea are worlds apart, so I have a call in to Les - the best trainer at the Y - to develop a fitness plan to maintain my lung strength until I can run again. If left to my own devices, I'll be there every day, biking 16 mph for at least an hour. I'm not entirely sure this is what the doctor had in mind, so I need to pick Les's brain and tap into his years of experience for good advice and planning.
Now the bad news: I can't run until I see the doctor again. He said 4-6 weeks and the receptionist offered me the very end of April. I asked for something earlier because I'm not going to delay running for weeks longer than I have to. Even then, it'll be back to the couch potato to 5K program, starting with running 60 seconds at a time...
The really bad news: Even before he knew what it was, the dr said absolutely not to the Martian. I'm likewise excluded from the mini indoor triathlon. Looks like my season will commence with the Dexter-Ann Arbor run, but instead of the half marathon, my target will be the 5k. Sigh.
Before I start running again, it would behoove me to have someone measure my legs and make sure they're both the same length. New Balance in Farmington Hills does a running clinic, so methinks I should head that way and have a running coach critique what I'm doing wrong, because it appears I'm doing something I shouldn't!