Hi Beth, my close relative had similar symptoms and a swollen lymph node on right side of neck. ENT did lots of inconclusive tests including USG Needle biopsy twice and finally excision biospy, which also came negative. It eventually turned out to be a rare disease for this part of the world. Its been 4 years since then and she's has been all well.

I would suggest changing the doctor. I hope your son is doing Salt water gargle atleast 4 times a day!