What Is The Cause Of Pain And Swelling Over The Gum In A Smoking Addict Post Root Canal ?

I have gum pain, sensitive to touch only (not hold or cold) in “extreme upper gum” next to nose. Teeth did/do not hurt when chewing or when tapped on. I have had the sensitivity there for appx 2 months but only when touching it. If I poked at it too much the pain would linger a bit but would go away (but constant when touched). There was no mass there. But the sensitivity was always there when I touched it. I have 4 bridges (all quadrants). I guess I have not had the best oral hygiene and I am a smoker. But I have had a lot of money spent on my dental work and the bridges have been in appx 10 years. FYI: I did have sensitivity in the upper tooth (#5) appx June 2011 but it went away. I went to a new dentist (in my new location) and he examined and took x-rays and said I need a root canal on #5. At least I think it is #5 (the one next to the vampire looking tooth). The root canal was completed yesterday and sealed permanently as he said it went well. He had prescribed me Cephalexin 500 mg (one capsule 3 times a day). I am allergic to penicillin. I have now taken my 7th dose of 21 capsules. I have had root canals in the past for which there was obvious pain in the tooth and gum and I always had tenderness afterward but always had immediate relief. I feel more pain in the “extreme upper gum” (same spot) now than I did before. I am taking motrin and the Cephalexin and the motrin is providing some relief. There now appears to be a “little” swelling/lump in that area of the gum. Is this normal? Should their still be abscess/infection there even after the root canal? Will the Cephalexin cure this by the time I have taken my 21st capsule (day 7)? Was this new noticeable swelling caused by the injection that was done right in that area? When should I become concerned or seek follow-up? The reason I ask these questions is because I am a smoker, have not had the best oral hygiene, this is not like other symptoms/root canals I have had, and I am concerned that it could be something else. I have been told that I may have allergies in the past, but I do not think so (maybe just some minor sinus issues, if at all). I know that had I went to my doctor for this first he would have sent me to the dentist anyways. Thank you