This is a developing traumatic fibroma,caused due to constant irritation due to cheek bite because of sharp tooth cusp i.e 3rd molar here.
You need an intra oral examination ,to get assure of the sharp cusp of that tooth.This doesn't go away on its own as long as the irritant gets removed i.e grinding of sharp cusp or better removal of that tooth 3rd molar causing this issue constantly & also this fibroma( benign mass) has to be removed surgically.Because this fibroma doesn't go away without surgical interventions as well as 3rd molar removal or grinding of tooth' s sharp cusp.
Next Steps
check for cheek bite( the 3rd molar causing this issue),get cusp grinding / removal of 3rd molar( in case it genuinely needs to be removed),surgical removal of mass( if its getting increase in size due to constant irritation)
Health Tips
visit nearby clinic for physical intra oral examination ,do luke warm saline water rinse.No need to fear,no issues of any gland problems as can be seen over the pics provided.this is simply a delevloping traumatic fibroma due to constant irradiation by the tooth here ( 3rd molar).