You should bring your child back to the doctor.
It is uncommon for a child that age to have any residual signs after that time period. Kids heal remarkably well.
There are several potential causes, all of which require a clinical examine. Persistent infection, fragment of tooth or bone, problem with adjacent tooth etc.... just to name a few.
Information contained within this reply is intended solely for general educational purposes and is not intended nor implied to be a medical diagnosis or treatment recommendation. This is not a substitute for professional medical advice relative to your specific medical condition or question. Always seek the advice of your own doctor for medical condition. Only your doctor can provide specific diagnoses and therapies.