Advice needed re root canal v extraction
 

Hello - I've been reading a few of these posts about dental issues and am currently trying to decide what to do.
Symptoms: pain comes on quickly in right upper back teeth - intensifies then seems to be 'referred' pain in lower right teeth. Lasts 5-10 mins then gradually disappears. Occurs up to 10-12 times daily (and at night).
Saw my dentist two days ago - x-ray showed cavity in second to last molar (although I thought the pain more located around the last molar - which has a crown). Dentist cleaned out decay and placed a temporary filling saying he thought it might be a root canal if the temporary filling didn't stop the pain - which it hasn't. He said he couldn't know for sure if it was the correct tooth canal until he had exposed it? I'm due to go back in 4 days time for another smaller filling and I'm sure the dentist will recommend the root canal but I am hesitant for several reasons. This would be my first root canal but friends who have had them have said they eventually failed and then had to have extractions. My main concern though is that I also have Primary Addison's Disease (Adrenal Insufficiency) and while both procedures would carry extra risk for me I'm not sure which in the long term would be less harmful. At present I'm tending to go straight for extraction. I have also read Byanna's advice about infections spreading to the sinus - I have had long-term problems with what I think is Staph A overgrowth in sinus/nasal/throat area but can I barely get 'medical professionals' to acknowledge there is a problem let alone investigate it. (the joys of public health service). I am also concerned that the dentist isn't 100% sure if the root canal is the cause of the pain or which tooth it's actually in. Does he just keep drilling until he finds the right one?
Thanks for taking the time to read this and appreciate any suggestions.