sister i found a good nhs link it may be helpful to you
Recurrent mouth ulcers
The cause of recurrent mouth ulcers is often unknown. However, there are a number of factors which may increase the chances of you getting recurrent ulcers. Some of these are outlined below.
* Anxiety.
* Stress.
* Oral trauma - such as excessive tooth brushing, or chewing sharp, or hard, foods.
* Certain foods - some people may find that eating certain foods can cause them to develop more ulcers. Foods that have been identified as increasing the risk of ulcers include chocolate, coffee, peanuts, almonds, strawberries, cheese, tomatoes and wheat flour.
* Hormonal changes
http://www.nhs.uk/conditions/mouth-u...roduction.aspx