I can understand your concerns.
It seems like your son has got Scalp folliculitis
which is the inflammatory condition of the scalp. One other condition that I can think of is Dissecting Folliculitis which is a bit rare and is more serious than the earlier condition.
It can also be an infected cyst
,I think at this point what I have gathered from your question that he needs to see a dermatologist
so that he can prescribe some antibiotics for him and also some anti inflammatory like Ibuprofen
would reduce the pain and swelling.
He can also opt to drain the enlarged cyst or lesion I it's needed.
A picture of the lesions would be more helpful but it's not there so I can't give you a certain diagnosis.
I hope this answer would be of some help.
All the best.