My right foot instep began to hurt, like after you kicked something hard (but I don't think I did). It's swollen and affects walking. Is it fasciitis?

Many possibilities. This type of pain canm be fasicitis, tendinitis or stress fracture. Arch supports, stretching and ice can help.
Possible. Fasciitis pain has classic symptoms. Morning pain or getting up after sitting for a period of time. It usually is not obviously swollen and can affect your walking. Shoes usually help with the pain and going without worsens it. Try ice, rest, stretching NSAIDS, and good supportive shoes. If no luck after a few weeks, see a Podiatrist.