The MRI of my foot didn't show a stress fracture in the 5th metatarsal. Good news! However, the hospital personnel who reviewed the scan diagnosed one in the second metatarsal. This wasn't what hurt pre and post Nationals and I have very little local pain there, so we think it may be an old injury showing up on the MRI. In high school I had soreness on my metatarsal pad, which was eventually relieved by a lift/pad we put on the bottom of my 3rd, 4th, and 5th metatarsals to take the impact off of the 2nd. Since we first put the pad on I've had recurring soreness as it gets compressed and when I've built it back up it stops bothering me (something I haven't had to do in 1.5 years, probably with the lower run mileage I've done with Triathlon) I was told I could run as soon as my foot didn't hurt. I ran for the first time last Sunday, 12 minutes. Everything seemed okay. I did two other runs on trails and grass, and today some intervals on the track, pain free. Well, my foot has been pain free, my lungs and muscles, not so much.
Now I need to sign up for a race for motivation!