It should be looked at asap.
Any idea on what it could be?
When was your last dental visit/x-rays? When was your last hygiene visit? You should definitely have it checked out.
Just like gameniac, your problem sounds like it could be related to an abscessed tooth (most likely the crown) either endodontically (nerves) or periodontically (gums) or a combination of both. It won't likely resolve completely on it's own unfortunately.
What can happen is that the nerve inside a tooth can die and abscess leading to drainage into the gums which creates the gum boil. It might bleed and can be purulent (pus releasing) or not. The other situation is if there is a localized area of severe periodontitis (gum disease). That can also result in a gum boil. The dentist will check out the area, take an xray and be able to tell you what can be done, either possibly a root canal ,deep scaling/curettage, extraction, referral, etc.
Well, I didn't think it would be an absess, because the tooth under the crown has had a root canal already. Although it is a double crown that is splinted, so it might have something to do with that, but it's beside the tooth that has had a root canal. That, and it doesn't hurt, so you'd think something like that would hurt. I go for regular checkups and cleanings, but I am due for my next cleaning in about a month. I could try and get in earlier though. Also, the swelling changes too, like it swells up after I eat something, or brush my teeth, then calms down a bit in betweem, hence why I just thought it was an irritation more than anything else.
So I went to the dentist, and they took some xrays. It was not an abcessed tooth, but they did see something there that needed to be cleaned out (no specifics on what) So he rooted around in there to clean out whatever was there, and now it feels like I have gums missing, although I'm sure it'll feel back to normal once it heals. No antibiotics, just let them know if there's any pain/recurrance of swelling in the next couple weeks, otherwise they'll see me in a month for my cleaning. According to the dental assistant, there was a lot of gunk in there that got cleaned out. Goes to show you that even if you brush twice a day and floss regularly, stuff can still happen.