Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concern... As per your complain and presentation of symptoms there seems to be problem associated with your submandibular salivary gland.. The swelling under the jaw at the time of eating which gradually resolves commonly occurs when the duct of the gland gets blocked with either a foreign body or a stone formed in the duct.. This leads to backflow of saliva into the gland as it is obstructed from coming to the mouth due to blockage.. As the salivation increases during meals therefore a swelling is evident at the time of eating.. This can be one cause.. But in case if it is not diagnosed exactly to be the cause then occurrence of a sore in mouth and swollen glands under the jaw can be due to allergic reaction to any common ingredient that you are consuming in food all the time.. If this is the case anti-allergic medication like Cetrizine or fexofenadine [allegra] can be advised. A blood test for allergic testing can be done to rule out the allergen. You should consult an Oral Physician and get evaluated and in case if duct blockage is found removal of stone either manually or surgically has to be done.. Hope this information helps.. Thanks and regards.. Dr.Honey Nandwani Arora.