I noticed a small pea sized or a slightly bigger round ball under my jawline, on the right side. i can move it around and it's sore, but not very. i have started dieting. what could it be?

Lymph node: If it's not growing huge, and not stuck to anything, chances are almost 100% it's a one of the normal lymph nodes, perhaps discovered as you lost a bit of the surrounding fat dieting. The average medical student discovers 2-3 in his/her neck / jaw area during the first year in school. Best wishes.

Swollen lymph node: Sounds like an enlarged lymph node. We have hundreds of lymph nodes in the neck. In general, lymph nodes greater than 1 cm in diameter are considered to be abnormal. They usually result from an infection or inflammation in the body. Usually they go away once the infection is treated. If the node continue to increase in size or does not go away after a few weeks it is prudent to get it checked.