hello. Welcome to HCM.
If your son has documented proof of primary complex, he should have probably responded. Sometimes, the organisms will be resistant to first line drugs, and you need to discuss with your doctor for second line therapy according to his age and presence of contraindications. It is also possible that the nodes are becoming secondarily infected. A complete work up including FNAC/ biopsy
for diagnosis and submission of pus for culture and antibiotic sensitivity would be helpful.