I had the same problem a 2 years ago. The dentist gave me a root canal on tooth next to crown. But the problem was the tooth with the crown. Now I have had both teeth pulled because root canal crown came off and was infected and the problem was the tooth with the crown. have your dentist x-ray before deciding to pull teeth. email ***@****
it needs to be checked and xrayed-- it could be an abcess from either tooth, or it could be gum tissue inflammation from a poor margin (especially since you said it never seated correctly)
You need to get an x-ray of those teeth, it sounds like one or both of those teeth need root canal therapy. it is also not normal for the gum to be inflamed, that too has to be checked out.