I had what felt like a blister appear just behind my front upper teeth one morning last week and then disappear just as quickly the next day. Very painful but healed very quickly.
Don't know what it was but since it came and went without good reason, I'm putting it down to the oil.
I've been OPing for about a month: 1 week with sunflower, 2 weeks hemp oil and currently Olive Oil.

That sounds like a good sign of detoxing...keep going and see what happens. Most people say that their detox symptoms come and leave within a few days.

I've only had one mouth sore, and that one just recently healed up. I know it was due to the toxins being brought up. It came out of nowhere...it hurt whenever I ate or had anything spicy.