Found out that I kept getting canker sores and versions of thrush from using mouthwashes. If you have c- sores and gargle with off the shelf mouth washes, try stopping for a few days. worked for me.
I used to suffer terribly with canker sores since childhood, till a friend recommended salt toothpaste - I obviously can't mention the brand here, but the main ingredient is baking soda and I have to say that for me (and the friend who recommended it) this really has been a miracle cure!
It's been many months since I posted this and I still have nearly no problems now. In addition to the above I switched to Jason Healthy Mouth toothpaste which has no sodium lauryl sulphate. I rinse out thoroughly 3 times with water after brushing, and that's all I ever have to do.
These days I get the occasional beginnings of an ulcer but it quickly disappears - usually within a day and causes me no pain. I would say I am cured.
P.S. for earth Clinic - why don't you follow all suggestions up with the original posters to see how they worked out in the long term? Most people post something here in a moment of excitement, but never come back to report their progress. An automated email with a form to fill in is so easy to do.
I suffered with mouth ulcers for 20 years or more. Recently I realized I wasn't rinsing well after brushing my teeth, and I know that sodium lauryl sulphate in toothpaste is an evil chemical known to cause mouth ulcers. So I decided to rinse my mouth out thoroughly several times (and gargle) with water after brushing. Since I've been doing that I have been free of mouth ulcers. We're talking about months, so I am very pleased.
I've also been eating a lot more omega 3 (in tuna/salmon/lamb). I see some people here recommend flax oil, so that might also be responsible.
I've had a lot of success with rotating toothbrushes. Make sure you have at least four toothbrushes and when you have canker sores brush your teeth four times a day, but never use a toothbrush more than once in 24 hours. This worked very well for me for about ten years.