Tooth pain / root canal

I had a root canal on lower left molar 3 weeks ago and it still has temporary filling. After 1 week then a lower right molar with a crown became very painful with a swollen cheek and pain in jaw and I just had a root canal on that tooth 3 days ago. Now I have an upper left molar that just became painful and the lower left molar with the root canal is also hurting. I am on penicillin and have been for about 2 weeks.

Am concerned because 3 teeth are now having problems. Are tooth infections contagious within my mouth and can this spread to even more teeth? Why is all this happening even tho I am on penicillin? I will call my dentist but wonder if he is givig me good advice and treatment if so many problems keep popping up. Should I see my regular doctor also. I thought the second root canal would end the problems so am pretty worried because more problems keep happening just as soon as we try to take care of the previous ones and it's also getting hard to keep on top of things in my life when this keeps happening.

[Jerome Tsang, DDS]

From my reading, I can only see two teeth, the one on the lower left that had a root canal and another one on the upper left which had a root canal before this lower left one.  

You should go back to your dentist to get it evaluated.  If they can't find whats wrong, you may need to see a root canal specialist.