Hi..
Welcome to HCM..
As per your query ulcers in mouth can be due to a number of causes and as you had them previously it can be due to causes like like Stress,
Nutritional Deficiency [Iron, Vitamin B12 and Folic acid] , hormonal changes, acid reflux, tongue trauma due to some sharp teeth or tongue biting habit, excessive intake of sour and citrus foods,
uncontrolled diabetes etc,,
As far as sore on the gum is concerned it can be due to causes like deep infection in the gum leading to gum abscess formation while it can also be due to deep decay in tooth leading to dental abscess..
Consult a Dentist and get evaluated and in case if ithe sore is due to gum infection deep scaling will help in resolution but in case if it is dental abscess then
root canal treatment of tooth has to be done..
For sores in mouth ulcer you can do warm saline gargles
Gargles with 1:1 solution of benadryl and
milk of magnesia can help..
Apply numbing gel over the sore for relief from pain especially during eating..
Take a multivitamin tablet for a period of 15 days..
Avoid spicy, sour and acidic foods..
Hope this helps..
Regards.