T.C.
If you're pregnant, your feet very likely would not be swelling yet. That's typically something that happens later in pregnancy and is a sign of pre-eclampsia or toxemia (if high blood pressure and/or protein in the urine are also there...if not, then it's just swollen feet).
I doubt your mind is doing it to your body. I think it's probably doing it for some real reason. Do you have high blood pressure or diabetes? I know things can happen to the feet if you have diabetes. Or if it's just super hot out there, it can be from the heat from the day before. Did you injure your foot? I don't know how old you are, but your body can react to things differently as you age. It sounds like an actual injury to me. It could be a stress injury or something from all the walking you've done. I'd give it a couple days and see if it gets better. Maybe it needs some rest. If it doesn't get better, or if it starts hurting a lot more, I'd go see the dr. FEEL BETTER!! And, I hope you end up prego soon if you aren't already (if you want to be, I haven't' read your other post).