Hello, Although, there is nothing to worry, that swelling is a mandibular Tori (A bony swelling) which is present on both sides (as visible in the picture). Sometimes, when you eat something hard, the gum over the bony swelling gets inflamed & cause pain. But still for confirmation of diagnosis, you can get the XRAy done & post the picture here.

Hi The pic u have attached and the description u r giving it looks like a mandibular tori ( a bony prominence) . If its getting a lil painful u can go for the surgical excision of the same. Please also attach an x ray image if u have.

It's might be because of tooth related infection .Also , your oral hygiene is poor & needs  to be corrected.