heres the thing:
what dentists today dont tell you(and pretend they dont know about is microbial bacteria being trapped within the tooth sometimes travelling to other parts of the body and creating other illnesses.
You need to do some reading on Weston Prices work:
[link to www.healingteethnaturally.com
check that sites out too its pretty good.
it does sound like you have an infection trapped in there.
Usually a normal dentists will clean out the roots(filing the canals) again and again until they'think' theres no infection left.
Antibiaotics sometimes dont work if youd had heaps of them or the infection type changes.
You can try some natural antibiotic remedies like taking colloidal silver, vitC/zinc, garlic,etc.
Youll know your really in trouble if you get an abcess that doesnt form a pimple on the gum and cant drain.
have the put a crown on the root canal?how many times have they filed/cleaned the roots?
did you have an abcess/pain before you had root canal?did it form an abcess that drained?