Hello and welcome,
Canker sores in mouth may have arised due to stress and hormonal changes like missed periods which you are complaining of now.
To prevent occurrence of canker sores,avoid anxiety and stress.
Maintain oral hygiene
Take fluids and nutritional rich diet.
Vitamin becosules and vit.c,iron and folic acid
supplements has to be administered.
To make your periods regular,take a balanced diet.
Avoid intake of fatty,baked food items.
Please do visit your dentist
as well as endocrinologist
for further reference.