Hi, It may be due to various reasons such as vitamin deficiency, intestinal infection and due to some immune response, stress and anxiety, hormonal changes in women etc. However after getting your case history I feel there may be some issue of stress and anxiety or vitamin deficiency. All these issues can result in aphthous ulcerations in mouth. However your case history is brief and therefore regarding treatment nothing concrete can be said. But I suggest you either share further details about yourself such as sex martial status, personnel life issues and any other medical issue and accordingly you can be helped or visit to some experienced dentist and get yourself treated properly. Prescribing medical prescription requires your further details as I asked for. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Sohail Hussain Zargar, Dentist