What could throbbing in the arch of ny foot be?

Plantar fasciitis? This pain can be quite severe and impairs ambulation. Fracture of the bone/stress fracture can cause severe pain as well, but not likely without trauma or excessive use-i.E jogging/running/jumping etc...It is difficult to tell for sure without examining your foot, but plantar fasciitis is likely. Use of arch support, motrin/aleve, stretching etc...If not better, consult doc.. Good luck.
Many causes. We need more information to be able to give an opinion on this, reasons can include, arthritis, plantar fibroma, callus, tendonitis, foot deformity etc, .
Pain. in the arch of the foot is typically inflammation or a tear in the fascial band. If there continues to be pain or throbbing that doesn't go away get examined by your Podiatrist for a definitive diagnosis and treatment plan!.Get better soon!