Its possible that the infection could travel and spread although the presence of a fistula is a good thing. The pus that is created is actually leaving the abscess through the fistula and preventing it from spreading usually.
The fever and headache can be from the infection of the tooth although if a root canal was performed, it should be fine. I would bring it up with your dentist tomorrow and discuss the possibility of some antibiotics for coverage and re-evaluating the problem in a week or so.
I wouldn't pull the tooth (because I'm very conservative and try to save all teeth) until all your treatment options are exhausted. Sometimes finances are a consideration though.
I went to my dentist and called my endodontist. Neither put me on an antibiotic because they feel I don't need it. I still have a headache and low grade fever -this is going on a week. I am getting concerned and am almost ready for the emergency room. How would I know if there is an infection in my body? Both dentists told me it couldn't happen. Thanks again.
If both the specialist and dentist feel that it isn't possible, then I'd go to your primary care physician to see what may be the cause of your symptoms.
As I said before, if the root canal was done, it should take care of the infection so its most likely not a cause but I understand that the timing of your fever and headache makes you believe so. Again, you should probably see your primary care physician to get it checked out.