Hello and thank you for your question.
Based on what you have described you have either a perio or a dental abscess
. This is causes either by a severe infection below the gum line associated with the gingiva
around the tooth or due to a tooth that has has the nerve
die and is now necrotic. Since the nerve is dead, you don't have any feeling in it and you won't experience pain. The reason why it doesn't hurt is because the abscess is draining and there isn't a build up of pressure. You need to go to a dentist
to get it evaluated and determine the origin of the infection to have it treated.
If you went to a dentist and they have no idea what it is, then I strongly encourage you to find another dentist and get evaluated. Most dentist know what this is right off the bat. This is normally treated by root canal
on the tooth, extraction or periodontal surgery with scaling, debridement and antibiotics.
Best wishes and good health