hello and welcome to hcm forum,
as you stated that there is persistent pain on the left side ,radiating to the head and neck,
also gums are swollen, it seems to be a case of acute infection,which may or may not be associated with erupting wisdom tooth, to clear out the diagnosis kindly get him checked clinically by a dentist
I would recommend, warm saline rinses or betadine
a complete course of antibiotic and anti inflammatory is also required.
It is highly recommended to visit your dentist.
I wish you good health,