I don't know if it is from the fast or not. What are you drinking? Juice? Water? I've gotten a yeast infection before because I my hormones changed. I think drinking lemon water helps. My system became too alkaline. I'm not sure that will be good for your canker sore. Lemon water might hurt.
Just keep flushing it could be from detox. Drink lots and lots of water. I've had sore kidneys before because I didn't drink enough. As soon as I upped the water the pain went away.
Thinking of you this weekend. I have only got 8 days to go. I cannot believe it!!! You can do it!