An indication of infection - quite possibly the start of an abscess - needs checking out because it can become very painful and untreated the infection can spread to your blood.
Oh, you should get to a dentist right away; I don't think it would be over-reacting to consider it urgent. You may have an abscess, which could become a serious problem left untreated.
Depending on your age and state of health there are many types of " Lumps " that may appear throughout your body, however a "lump" "on" your Scrotum is of importance regardless of age or health...