Hi..
Welcome to HEALTHCARE MAGIC..
I have gone through your query and can understand your concerns..
As per your complain and presentation of symptoms a bump under the jaw that increases in size on eating occurs due to obstruction in the duct of the sub-mandibular
salivary gland by some foreign body or formation of crystalline stones [SIALOLITHS] from the minerals present in the saliva..
These stones obstructs the flow of saliva from the salivary gland to the mouth and the saliva flows back into the gland and the gland expands leading to swelling..
The swelling becomes more prominent during eating as the saliva flow is more during eating..
You should consult an ORAL PHYSICIAN and get evaluated and in case if the stone is superficial in the duct and is located in the floor of the mouth the physician can palpate over the stone and remove it by pushing it towards the duct opening..
Deeper located stones can be located by SIALOSCOPY which is an endoscopic technique and can be removed surgically..
Hope this information helps..
Thanks and regards..
Dr.Honey Nandwani Arora..