Why would a foot be swelling and hurting all the time when you walk?

Many things: There are a number of things that can cause swelling in the foot . This is a very nonspecific symptom. I recommend that someone with swelling should be seen by orthopedic foot and ankle surgeon for a definitive diagnosis. One in your area can be found at www.Aofas.Org.

Stress Fracture???: It could be a fracture (broken bone) a sprain (torn ligaments) or a strain (strecthed out ligaments). Have a physical exam by a podiatrist to make sure which one it is and follow the treatment recommendations. Sometimes, just a compressive wrap is needed, maybe a splint or a walking boot. It's tough to say exactly without an exam.

Maybe it's broken: You could have a stress fracture. Other causes could be tendonitis, neuritis. Please see a foot doctor for proper evaluation and treatment and stop walking in pain.