So I went to the doctor, and got some x-rays of my foot and all, and apparently there's nothing wrong with me. I guess I'm a little disappointed that they couldn't find anything wrong, and moreso because I feel like they didn't really try. The doctor said it was probably "normal wear and tear."
I wasn't able to see the orthopedist that I wanted to see, because you have to go to a regular doctor first. I wanted to see him because he works with athletes and might have some input on why I've gotten injured and maybe I could ask some questions about running and training and stuff.
The doctor I did see actually told me that "running marathons is great and all, but it's not really what we're meant to do." I didn't feel like arguing how our long legs, springy feet, and large buttocks are specifically designed for running long distances (Bramble and Lieberman, Nat'l Geographic summary). So, she might have well have told me to "ignore whatever I say that you don't like."
But at least I got some x-rays and it's clear that there's no fracture, and I think if there was some subluxation of the cuboid, that would be visible on x-ray too, so I guess that's not it either. Those were the two worst case scenarios that were keeping me from running, so even though it still hurts a little I did an easy three miler this evening.
Keep on keepin on.