3 months ago, I had a root canal performed on my molar and put a crown
on it.  It was fine until last week when it's starting to ache badly.
The source of pain is the gum (on that tooth) itself.  If I put my
finger on the gum and press, the pain intensifies.  I couldn't chew on
that side of the mouth anymore.

How can this be?  Didn't the root canal took care of the nerves?  It
was fine for 3 months.  Is this related to my jaw clicking?  It's on
the same side of that tooth.

I would like to get some ideas first before going back to my dentist
so I could make better decisions.