Hello and hope you are doing well.
It could be due to Quinsy, which is a peritonsillar abscess, that is there is pus collection around the tonsils. But with this he will have systemic symptoms like fever and he will be toxic. This is an emergency and needs to be treated with IV antibiotics. Sometimes it warrants incision and drainage of the abscess. It is also an indication for tonsillectomy. Please contact your concerned physician at the earliest to rule out this condition.
Hope this helped and do keep us posted.