Lymphnodes do clog. God bless doctor ingorance about lymphnodes. This may mean that your child has lymphedema. I do not know where you live but it would be wise to find someone who specializes in child lymph massage. The back of his head and neck should be opened up with massage so the lymphnode can drain.
Regular doctors do not know much about lymphedema or lymphnodes. It can be scarey but you can learn to drain it for you son when it happens. Watch for other face, neck, shoulder swelling. The head nodes drain from the back of the neck. It could cause him to have trouble hearing or headaches.
Do not get depressed and feel that life is over. This is very manageable. It is not your fault. Sometimes it is infection or an injury. I was born with the problem but I was in my thirties when it became unmanagible.