I been having recurrent aphtous ulcers for many years. Otherwise no other symptoms or past medical history. Pls give advice on reducing the frequency?

Check for trigger. Recurrent aphtous ulcers or canker sores can be caused by a number of triggers or initiators. These lesions are not bacterial or viral origin. Stress, trama, weakening from illness, food additives or colorings or flavoring, wine, nuts, etc. You should journal your food and drink intake, habits, and dates to determine if these occur after certain times or job or school schedules, or intake.
Behcet's? Consider visiting your doc regarding this. More than likely this is nothing, but there is something known as behcet's that can cause similar symptoms. Your doc should be able to advise you on this more - may be off base completely.