root canal questions

I had a root canal performed on two sides of my mouth in 2008. The teeth that were worked on, fell out since I did not have them worked on. Now, it feels sore on the left side of my mouth. The pain started today, and hurts when I try to eat.

I like to know if root canals can cause any health problems? I never had any health problems until the root canal. I have hypothyroid.