Baby only has ONE palpable lymph node on his head!!

My son is 5 months old, and since I can remember, he's had one palpable lymph node on his entire head. It's hard to the touch, about the size of a pea, but it does move under the skin. I've felt his ENTIRE head and he only has this ONE! I circled the area where it's located in the picture. Out of his entire head, there's just this one lymph node. Any other mommies notice this in their babies? I'm such a worry wart and I'm SO quick to jump to conclusions.