My son is 3 now. Last year we went through something similar. In Feb we noticed a lymph node - very prominent. He had just had the flu, so I didn't stress too much. But 2 months later, he still had colds, and still had the node.
He was also very pale, and a lot of the time didn't eat.
I saw the dr, and he said he thought it was a normal node. But he would schedule an ultrasound and take it from there.
I was very worried - and the ultrasound was 2 months away. He had 2 other nodes also - including one near his collar.
Well he had the ultrasound last July. The node was normal - just a superficial (near skin) node. Normal for kids. He had one the same size on the other size., but it was deeper so I couldn't feel it.
Fast forward 6 months. He is still fussy. Still gets cold. And the node is still there - but not as worrying since I know what it is. I sure your son is the same.