Contact your dentist and inform him about this matter. Get an IOPA (radiograph) taken of that area. It may be because of a left over root tip, or infected tooth beside the extracted one. Only by taking a radiograph can we know for sure.
Health Tips
Take Ketorol DT tablet thrice daily after food for the next few days and take Pan D capsule twice daily half an hour before food for the same duration. The first dose of Ketorol DT, take 2 tablets together at a time, and then take 1 tablet subsequently.