You could have gotten something stuck under the tissue which created a local area of inflammation. (popcorn hulls are notorious for this) If this is the case a dentist can prescribe an oral rinse that will help. In the meantime, continue to brush and floss the area to keep it clean. Make sure you're flossing behind the wisdom tooth. Warm salt water rinses may help. The worst case scenario would be an infection. To know for sure you would need a x-ray of the area.