Hi aphthous ulcers are due to vitamin deficiency… supplemnt with vitamin rich diet food   along with capsules for cople of weeks you will be fine…  It could also be due to viruses infecting oral cavity are herpes  infection, HPV infection, coxsackievirus infection, mumps,  measles (rubeola), and rubella.... consult physician for antimicrobial mouth wash and cream, steroid creams.... avoid spicy, salty, or acidic foods, use a soft toothbrush to avoid irritation..