Canker Sores!!

So my boyfriend and I have been raw for a while now. Every morning we would break our 12 hour dry-fast with a huge huge glass of lemon water as soon as we woke up. We had to stop this because we found a direct relation to canker sores:
Even a 1/4" slice of lemon squeezed into a glass of water = Canker sores the next day!

This happened before we went raw as well. Scince we stopped adding lemon juice (we also tried subbing with lime juice, still a problem) we have been avoiding high-citrus fruits and haven't had a ton of problems, but we still average on about one sore every two weeks, each. They're extremely uncomfortable! I feel especially awful because Jesse gets them very badly. (His ulcers sometimes literally get up to a full inch wide! :( )

We have heard of oil pulling, but after he learned that it will make it bigger before it got better, he instantly pushed that idea aside.

Any thoughts or reccomendations?

PS. I couldn't seem to find a health related section to post this question?