root canal post pain

3 months ago I had a root canal.  I had more pain after the procedure than the pain I was experiencing before the root canal.  The endodontist tried a round of antibiotics but to no avail.  I was having extreme heat sensitivity (none prior to the root canal) and pain when the tooth was tapped.  6 days ago the root canal was redone.  The heat sensitivity is gone now but I have increasing pressure pain.  Sometimes throbbing.  I was not put on any antibiotics yet and have not contacted my endodontist because he was a little unclear on his instructions as to how long I might have some discomfort after the procedure.  I do not want to be a troublesome patient, but definately have concerns that there is something more going on.  When I bite down I also have pain and pressure.  The tooth feels unstable.  What could be going on and do I need a course of antibiotics?  How long should I give this before contacting the dentist?

[shouldi]

I have 3 back molars that need root canal but Ihave decided to get them pulled out which they are tomorrow. My oral surgent was honest with me and told me that root canal does not always work and a majority of times the proccedure needs to be do again years later. He suggested that I just get the molars extracted for 2 reason.
1. The tooth will no longer be there to bother me anymore.
2. When a tooth is extracted the root and the nerve are both killed.

I suggest just have the tooth extratced.