Any health experts?

[hlcn8]

you have lymph nodes all over your neck, as well as under your chin, and at the jaw articulation, which is the location you described!

[bad14u]

FB, the area you are pointing out has two 'submental glands' there, so that could be the culprit.

Lymph nodes, which reside throughout the body and are prominent around the jaw and neck, are the gathering sites for white blood cells and other cells that help fight infection. Typically, infection results in swollen and somewhat painful nodes.

[Shibby]

Where would our lives be without google.

[FitnessBrat]

Thanks guys - I'm sure that's what it is. :)