The condition you mentioned indicates you have crowded teeth which further creates inability to cleanse that area properly with brush, making it more prone to gum infection and ulcers could be due to improper placement of your corner teeth. the best thing would be to visit an orthodontist as it would require proper alignment of your teeth with braces.
Next Steps
please visit a dentist or orthodontist. A whole mouth radiograph (OPG) would be advised to check the proper position of corner teeth and further treatment planing of your corner teeth
Health Tips
for now you can use mouthwash twice daily, brushing twice a day morning and at night before going to bed. for your ulcers apply Mucopain gel 3 times a day to alleviate pain.
take care