What Causes Lumps In Neck With Enlarged Tonsils?

Hi ther emy son has a very bad cold that just doesnt really clear up its been 2 months now and now he is on antibiotics for his enlarged tonsils, what concerns me is that he has lumps just behind the neck mucsles in both sides of his neck and one lower down towards the collarbone most of them can move around, they usually go away and just come back again even when he just has a slight runny nose. What could this be, we had him at the dok and he said give it a few days and if they dont go away bring him for blod tests but usually they go away and just come back again