Why do i get a discomfort under the right side of chin area sometimes.. its there then it goes away for a while then it comes back again, usually feel it when moving my mouth in a certain way.. worried? is it serious?

It is best you get evaluated physically because there is not enough information to confirm what it is, and how serious it is. As people get older the immunity goes lower and that may predispose to increased chances of mouth infection. You have not definitely indicate the location however it could be your salivary gland or a reactive lymph node to oral infection. If you smoke get evaluated soonest.