After novacaine, can't open my mouth much

Hello,
I had a root canal on a lower molar (#20, i think) in feb 2010. It is now August 2011 & that tooth has abcessed. I had it pulled a few days ago & a lot of the pain & swelling has gone. There is still a hard lump, but I'm only on my 3rd day of antibiotics.
My first question is, shouldn't a root canal last longer than 18 months? I felt at the time that they didnt do something right?
But my main question is, when they gave me 3 shots of novacaine to pull it- could they have hit a nerve? I can only open my mouth an inch. Or is this just due to the location of the infection- because the hard lump is right at my jaw line? Either way, when should it be back to normal?
Thank you for your help!

[Jerome Tsang, DDS]

Usually a root canal should last longer but it can depend on a case by case basis and it never necessarily means that all root canals should last years.  

The limited opening may be due to the infection and should start to improve as times goes on.  I would guess that after about a week or so, it should start to get better and should be back to normal within a month.