Why is the tooth adjacent to a dental bone graft becoming increasingly painful?

Had bone grafting done on right lower jaw Aug. 27. Since then the tooth next to the graft site which covers an area that once held 3 back teeth, has become very painful to the touch and it throbs constantly despite taking Ibuprofen. The graft site is still swollen and a bit tender but not excessively so. However, the tooth adjacent to the graft area is extremely painful.