For now take a pain killer to relieve ur pain...and consult a dentist near by as early as possible and get a checkup done with proper radiographs (x-ray) to diagnose your problem. It could be because of
1. Wisdom tooth
2. Decayed tooth or
3. Any trauma from occlusion,etc.
Next Steps
consult a doctor asap and seek early interventions
Health Tips
Along with medication also do warm water gargling with a pinch of salt added in it.