I have suffered chronic mouth ulcers for 12 years attended many doctors to try find the cause only to be disappointed as they can't help..any ideas?

An Idea: Most mouth ulcers are a herpes type. Some chronic cases of this (if this is what it really is) can be treated by having an injection made from a deactivated and weakened version of the virus. Some research hospital could probably help you find a place that does this. It may be worth a try.

Lysine deficiency: It may be simply a need for lysine. Also i would ask about your diet. Does it consist of lots of acidic foods. Stress will also initiate these ulcers as it compromises your immune system allowing the dormant strep bacteria to produce mouth ulcers.

Autoimmune?: If it has been that long, you may want to see a rheumatologist. Behcet disease can present with mouth ulcers and pemphigus also.

Decrease acidity : Some patients with recurrent mouth ulcers have saliva which is too acidic leading to an unhealthy environment in the mouth and resulting ulcers. First of all stop eating and drinking acidic foods and drinks. No coffee, tea, soda tomatoes, orange juice etc. Get some liquid antacids and rinse with 1 tablespoon after each meal and before bed. This should help a lot.