Hello from your symptoms it is more likely to be lymph node enlargement or submandibular gland infection. If doesn't come down  get usg neck Not a serious problem, but needs treatment Take care

From the detailed you have given , and history of repeated episodes swollen lymph nodes mostly are seen associated with infections rather than any malignancy/ cancerous lesions . Also a group of salivary gland called sub lingual salivary gland are also palpable just below your jaw slightly toward the lateral side , what you are palpating could be this gland which is normally palpable . If you are having serious concerns we can consider going an ultra sound scan of your neck , which will help us rule out any suspicious lesion . You can consult me anytime if you want any clarification regarding this

Hi   It is probably reactive lymphnode due to some infection or inflammation. Please see a doctor if it doesn't subside after antibiotics

Any mouth ulcers previously ... Mostly probably inflammatory node.. No need to worry Kindly consult a doctor for examination....