I don't think so. It's on the inner side of my teeth/gums, I'd need some sort of mirror set-up that I don't have
In the absence of diagnostic information, there are several potential diagnoses that are suggested by your description.The first and most likely is a normal anatomic variant known as a "torus mandibularis". This is suggested by the location, and your characterization of the lump as being "rock hard". The consistency implied by that descriptor could only represent a growth of bone, because the hardest bone or epithelial-derived lesions do not begin to approach that level of hardness. Where your description begins to part company with a torus mandibularis is your report that you "...can move it around a little bit", because tori are fixed to the mandibular bone, and are immovable. Because of this, some additional factor would seem to apply. In the case of mandibular tori, scrapes and cuts are common, because the gum tissue overlying them tend to be thin and often sustain friction with food during chewing activity. Therefore, a torus with perhaps some local tissue trauma would be my first guess. Torus mandibularis does not require treatment unless its presence interferes with the placement of a denture, in which case it may be surgically re-contoured.
You can see a picture of torus mandibularis here:
Rarely, a fistula from a nearby tooth infection can drain to the gum surface in this area, but most fistulae are neither hard nor painless, and I include this for the sake of appearance. Other lesions that should be considered, although much less common, are epithelial neoplasms such as papillomas or keratoacanthomas, as well as granulomatous or infectious lesions (sarcoid, tuberculosis, or chancre). Malignancy would be very uncommon in this particular area, although salivary gland neoplasms do have some precedent here.It is unlikely that your sore throat or lymph node are related to the lesion unless it represents infection; the lymph nodes in the neck do tend to become enlarged and tender in the presence of dental infection.Hope this helps...