Hi scooby,
Why don't you phone the out of hours service at your dentist ?, they can drill a hole in the tooth and then put an anti-biotic into the root, if it is quite bad though it may mean the tooth being taken out and a crown fitted,the normal anti-biotics they prescribe normallly kick in within about 24 hours,if it is a 5 or 7 day course, root canal is not very nice,but they don't often get the wrong tooth,give them a ring now, you could try to put some bonjella or similar remedy on to relieve pain a bit,hope it feels better soon, Ray