Any pus coming from the area.........?
Sounds to be an insect bite. My thoughts come to that of a tick. Most often these will look like a bulls eye target with a dot in the center. If he is running no fever at this time and continues to have it tomorrow then I would suggest to have him seen by a doctor for a check of it. Tick bites can carry lyme disease. It could also be the beginning of a boil or carbuncle. Reply if needed.
Let me add to use a warm compress for the time being and see if this helps with the symptoms.