Plantar fasciitis might be another cause. Now that I think of it, that may be what you were referring to in #2. Fascia is the tough membranous connective tissue that thickens to form tendons and ligaments, and plantar refers to the underside of the foot. (Yeah, that would probably cover "tendons in the bottom of my feet".) It usually shows up in connection with heel spurs, too.

Sorry. Voices from my massage therapist past.
I'll stop boring you now.