My left foot on top hurts. Walking on it is painful and feels like it's going to pop?

See doctor. Could be a fracture, stress fracture, tendonitis or other cause. You may need an x-ray.
Inflammation or.... Do you notice any swelling or discoloration ? Has there been any recent injury and has this ever happened before? I would be thinking either inflammation, tendinitis or possible stress fracture. Until you can be evaluated, i would rest and elevate and use ice on the top of your foot. Limit any weight bearing or strenuous activities on your foot. Xrays will help to identify any fractures, etc. -h-.